Anil, adding medical words is helpful, but it does not address the "ignore mixed cap" bug which to me severely hobbles the spell checker.
Bert, we are all holding our breath -- ver. 6.5 is coming! All prayers will be answered.

Still praying. I basically think you are just stuck with this spell check.
Looks like you are both right. V6.5.5 has a spell checker in the letter writer which is apparently independent of the old one. That means that any letters you generate will be done with a functional spell checker. In fact, it may be worthwhile to use Anil's approach to increase the vocab there.
The bad news is that the spell check in the notewriter is unchanged.