Could a Betazoid (skilled or otherwise) read the feelings or thoughts of a Trill symbiont? Is there any evidence in the canon that this is possible?
TNG S4E23 The Host has this dialogue:
PICARD: Counsellor, what is it?
TROI: It's Ambassador Odan. I continually feel fluctuations of emotion from him.
PICARD: Perhaps it's perfectly normal among the Trill.
TROI: It could be. We know so very little about them.
PICARD: Yes. Quite.
Unfortunately she says little else about him, but this does make it clear that (half-Betazoid) Counsellor Troi can at least partially feel the emotions of (Trill) Ambassador Odan, so the Trill are not completely immune to Betazoid empathic abilities.