Yes, you can still use it for all previous games but you will have to ignore certain Pokemon if you depending on what game you are playing.
If you are playing White 2, ignore these Pokemon, along with Hoopa, Hoopa Unbound, and Volcanion.
If you are playing White, ignore these Pokemon, along with Black and White Kyurem.
If you are playing SoulSilver or Platinum, ignore these Pokemon, along with the Pokèmon listed above.
There are more things that will be different too:
Some Pokemon might learn different moves on different levels. (Credit to Meewec.)
Fairy type didn't exist, so some Pokemon will have different typing:
Cleffa, Clefairy, Clefable, Snubbull, Granbull, and Togepi will lose their Fairy typing and become Normal type.
The Fairy typing of Mawile, Ralts, Kirlia, Gardevoir, Cottonee, Whimsicott, Mime Jr., Mr. Mime, Igglybuff, Jigglypuff, Wigglytuff, Azurill, Marill, Mzumarill will completely go away making them pure [whatever type they are].
Togetic's and Togekiss's (Wow, 3 Ss in a row, it's a new world record.) Fiary typing will turn into Normal type, making them Normal and Flying type.(Partial credit to Sapph)
Mega Evolutions and Primal Reversions will not exist.
The below things are not Pokèdex related, but they may be of some use to you.
The following moves will not exist if you are playing Black/White 2:
Dragon Ascent, Hyperspace Fury, Precipice Blades, Origin Pulse, Aromatic Mist, Baby-Doll Eyes, Belch, Boomburst, Celebrate, Confide, Crafty Shield, Disarming Voice, Draining kiss, Eerie Impulse, Electric Terrain, Electrify, Fairy Lock, Fairy Wind, Fell Stinger, Flower Shield, Forest's Curse, Flying Press, Freeze-Dry, Geomancy, Happy Hour, Grassy Terrain, Ion Deluge, Infestation, King's Shield, Hold Back, Magnetic Flux, Land's Wrath, Misty Terrain, Mat Block, Mystical Fire, Moonblast, Nuzzle, Noble Roar, Oblivion Wing, Parabolic Charge, Petal Blizzard, Parting Shot, Phantom Force, Play Nice, Play Rough, Spiky Shield, Power-Up Punch, Powder, Rototiller, Topsy-Turvy, Sticky Web, Venom Drench, Water Suriken, Thousand Arrows, Thousand Waves, Light of Ruin.
The following moves, along with the moves listed above, will not exist if you are Playing Black/White:
Freeze Shock, Ice Burn
The following moves, along with the moves listed above, will not exist if you are playing Platinum or HeartGold/SoulSilver:
Hone Claws, Wide Guard, Gaurd Split, Power Split, Psyshock, Venoshock, Wonder Room, Automize, Rage Powder, Telekinesis, Magic Room, Smack Down, Storm Throw, Flame Burst, Sludge Wave, Heavy Slam, Quiver Dance, Electro Ball, Synchronize, Soak, Flame Charge, Coil, Low Sweep, Foul Play, Acid Spray, Simple Beam, After You, Entertainment, Chip Away, Echoed Voice, Clear Smog, Quick Guard, Stored Power, Ally Switch, Cleear Smog, Scald, Hex, Heal Pulse, Shell Smash, Circle Throw, Shift Gear, Incinerate, Acrobatics, Quash, Sky Drop, Retaliate, Reflect Type, Bestow, Final Gambit, Inferno, Fire Pledge, Water Pledge, Grass Pledge, Struggle Bug, Volt Switch, Frost Breath, Dragon Tail, Work Up, Electroweb, Bulldoze, Wild Charge, Drill Run, Heart Stamp, Dual Chop, Horn Leech, Sacred Sword, Leaf Tornado, Razor Shell, Heat Crash, Steamroller, Night Daze, Psystrike, Cotton Guard, Hurricane, Tail Slap, Head Charge, Techno Blast, Searing Shot, Relic Song, Secret Sword, Glaciate, Bolt Strike, Fusion Bolt, Blue Flare, Fusion Flare, V-Create, Snarl, Icicle Crash
The following items will not exist if you are playing Black/White 2:
All Mega Stones, Red Orb, Blue Orb, Adventure Rules, Ability Capsule, Assault Vest, Discount Coupon, Dowsing Machine, Elevator Key, Holo Caster, Honor of Kalos, Jaw Fossil, Sail Fossil, Kee Berry, Looker Ticket, Lens Case, Luminous Moss, Lumiose Galette, Mega Ring, Maranga Berry, Pixie Plate, Power Plant Pass, Prof's Letter, Roller Scates, Roseli Berry, Sachet, Whipped Dream, Saftey Goggles, Sprinkletoad, Snowball, Strange Souvenir, TMV Pass, Weakness Policy, Common Stone, All Mulch, Ability Capsule.
(Note: The Dowsing Machine is Different between most games, that is why it it listed on the items that do not exist in White 2.)
The following items, along with the ones listed above, will not exist if you are playing Black/White:
Colress MCHN, DNA Splicers, Dropped Item, Grubby Hanky, Medal Box, Oval Charm, Shiny Charm, Reveal Glass, Plasma Card, Permit.
The following items, along with the ones listed above, will not exist if you are playing Platinum or HeartGold/SoulSilver:
Douse Drive, Shock Drive, Chill Drive, Burn Drive, Evolite, Prism Scale, Sweet Heart, Air Balloon, Rocky Helmet, Float Stone, Red Card, Absorb Bulb, Ring Target, Binding Band, Cell Battery, The Elemental Gems, Eject Button, Wings, Cover Fossil, Plume Fossil, Dream Ball, Pass Orb, Liberty Pass, Poké Toy, Prop Case, BalmMushroom, Dragon Skull, Comet Shard, Big Nugget, Pearl String, Relic Copper, Relic Silver, Relic Gold, Relic Vase, Relic Band, Relic Statue, Relic Crown, Light Stone, Dark Stone, Xtransceiver, Gram 1, Gram 2,
Gram 3, Casteliacone, Greet Mail, RSVP, Favored Mail, Thanks Mail, Inquiry Mail, Like Mail, Reply Mail, BridgeMail S, BridgeMail D, BridgeMail T, BridgeMail V, BridgeMail M.
HeartGold/SoulSilver items that will not be in Platinum:
Apricorns, Lure Ball, Level Ball, Moon Ball, Love Ball, Friend Ball, Heavy Ball, Fast Ball, Sport Ball.
I think I'm done, tell me if there's anything I'm missing.
(Sorry I have taken a few days to complete this, I've been having power problems recently.)
Hope I helped!
I have listed them above.