No.
1. Most GBA games are too large to work well online.
2. I am not big fan of the GBA games being here at all since they are too new. I have often thought about removing them all together.
3. The emulator is not being developed and so new games can not be added - except some large games - see #1.
Another problem with having a GBA Pokemon game hosted here would be saving. As of now, the GBA emulator on this site won't allow saves. Otherwise, I might be playing Advance Wars more often. I mean, how can you play Pokemon without saving? You'd have to be some insane speedrunner or something.
I had a Poke Blue cartridge that went through the washing machine in someone's pants and it lost the ability to save (and I was this close to beating it too...). The game became instantly not fun.
Well, like I said, I just wanted to try it and see if it was different the red/blue and if it was good.
And I had Pokemon Red and it went through my washing machine and also lost the ability to save...but when Pokemon Crystal was washed, no effect.
Well, on the plus side, you can still play Red through Crystal, with a few variations (Green, hacks, etc), and those save. But yeah, unless they make a better Java GBA, that'll have to do for your Pocket Monsters fix.
BTW, once GBA gets save states and Kong can add new games, I'd personally like to see Fire Emblem: Fuuin no Tsurgin (sp?, it means Sword of Seals, or FE6) playable here.