Hi Aaron,
Yes it's possible to apply expressions in the Relevant column for repeats.
We should be able to apply the expression to the repeat as a whole (hiding the repeat) or questions within the repeat. Here is more information on how to apply relevant expressions:
https://community.esri.com/t5/arcgis-survey123-blog/the-art-of-hiding/ba-p/898454
Constraints are a separate item, preventing users from submitting values unless the constraint is met.
If you're still encountering difficulty, can you please attach your XLSForm?
Cheers, Chris