Had tried using many spell checkers for Flash UIComponents but none of them work.
Fortunatly there was one it self from Adobe Open Source (Adobe Labs) Squiggly
Which does all which is needed. but there are some loop holes and you have to handle garbage collection your own way or else client system will stole, take 50% of CPU memory..
So if your useing squigly for large project which involve Runtime genration of UI component make sure it has been disabled after use.
Hope this helps.