Yeah. Idkw else to put :3
Yes, yes you can!
All those games are compatible with each other.
Using the Game Link Cable you can connect two consoles containing either of those games, and you can get both games to enter the Union Room. It is there you can trade. :D
Hope I Helped. :)
both are generation 3 games allowing trade
In order to unlock trading from R/S/E to FR/LG, you need to complete the Ruby and Sapphire sidequest found after you have beaten the champion in you respective FireRed/Leafgreen game. Only then can you trade between all of Generation III. This was done so that no Johto/Hoenn Pokemon could interfere with the spirit of the Generation I games that FireRed/Leafgreen was trying to emulate. At least, before the post-game.
Hope I helped! =D