Ninetales has 76 physical attack and 81 special attack, which I think is slightly below average. Its biggest problems are typing and movepool. Fire is particularly bad in Emerald, where water type opponents are very common. Its movepool consists of fire attacks (which would be useful, but this game has very few grass, bug, and steel Pokemon), normal attacks (which are not super effective against anything), dig (which has 60 base power), feint attack (which has 60 base power and takes a long time to get), and iron tail (which is super effective against 2 relatively uncommon types). This is how useful it would be in each major battle.
Maxie: His Camerupt resists fire and knows earthquake.
Tate and Liza: Their Claydol knows earthquake, their Lunatone and Solrock resist fire and normal.
Archie: neutral matchup
Juan: All his Pokemon are water type.
Sidney: neutral matchup
Phoebe: neutral matchup
Glacia: 3 of her Pokemon are water type and have thick fat, and her Walrein knows surf.
Drake: All of his Pokemon are dragon type, and 4 of them know a super effective move.
Wallace: All of his Pokemon are water type and know a powerful water attack.
A Pokemon with slightly-above-average stats and no good type matchups is probably not worth using. Blaziken is much better.
