Yes. Whom cannot be the subject of "are necessary: it has to be "who".
"... there are lawyers you feel who are necessaryto the transition of your practice, ..."
or "... there are lawyers who, you feel,are necessary to the transition of your practice, ..." "you feel" is in parenthesis and can be omitted.
I hope everyone is comfortable with 'who' there, because I always change it. That is, I hope there's no-one for whom 'who' is actually ungrammatical. However, 'whom' is very common among careful speakers, and has been defended as a valid alternative by the highest authorities (Jespersen and Huddleston & Pullum).
Entangledbank, I agree that there are cases when whom is the correct pronoun and who is not. For instance, if the sentence were "Also indicate whether there are lawyers whom you wish to add to your team," I'd be fine with whom.
I was surprised by entangledbank's suggestion that a sentence such as "Also indicate whether there are lawyers whom you feel are necessary to the transition of your practice" might have defenders among careful speakers and some authorities, so I tried to verify it. The section "Ambiguous cases" of Wikipedia's article "Who (pronoun)" does cite some defenders of the idea that this use of whom is grammatical rather than a hypercorrection.
I myself would avoid the use of whom in such constructions.