I don't think someone could placate you out of jealousy even if they wanted to
. And that's not a reaction to you, just to the issue of jealousy.
But if you mean you're looking for a therapist who you will not worry is judging you, then it's a totally reasonably idea. You want to be with someone you really feel comfortable talking to, and someone who is open to whatever option might work best for you.
I see no harm in asking your therapist about an underlying bias and whether she thinks it might get in the way. Also no harm in telling a therapist you're feeling apprehensive about her response, if that's an issue.
I think therapy has helped me deal with jealousy, although it wasn't an issue I went in to address. (That would be: I need to stop falling in love with people since I'm already married. With tremendous luck I picked a poly-friendly therapist, so ended up approaching a lot of issues differently than I expected.)
For me, sometimes useful questions in dealing with jealousy are the "why" questions: why do you want that, why do you feel insecure, why do you feel distrustful. It helps to step back and assess whether my feelings are linked to the reality of the relationship or more to my own individual issues.
It's still hard at times though, and I have also wondered whether I'm just not up to the challenge, so I sympathize with your dilemma.