Based on the video here [1] and some of the links on that page, plus assorted diagrams of other bulk acoustic wave resonators, I don't think there will be any problem.
Helium can interfere with devices that either depend having a vacuum in a volume or depend on having that volume contain a gas mixture with specific properties. Helium getting in messes that up.
The BAW on-die-oscillators do not appear to have any places that are supposed to be vacuum or supposed to contain gas. The have two piezoelectric thin films, with acoustic reflectors behind them. The gap between them appears to be solidly filled. All the relevant acoustic waves are carried in that solid stuff, not in air. (This also means, I think, that these things should be OK in vacuum).
Helium can interfere with devices that either depend having a vacuum in a volume or depend on having that volume contain a gas mixture with specific properties. Helium getting in messes that up.
The BAW on-die-oscillators do not appear to have any places that are supposed to be vacuum or supposed to contain gas. The have two piezoelectric thin films, with acoustic reflectors behind them. The gap between them appears to be solidly filled. All the relevant acoustic waves are carried in that solid stuff, not in air. (This also means, I think, that these things should be OK in vacuum).
[1] https://training.ti.com/tis-bulk-acoustic-wave-clocking-tech...