I am about to try this out because…
I currently have SherpaTTS installed (and previously tested RHVoice). Neither of these work reliably and fully with AA with stubs installed. I get some TTS functionality for maps but I haven’t been able to get any STT to work for them (despite SherpaTTS at least reportedly be capable of doing so - I need to test it on phone alone to validate); they seem to be incompatible with the SMS messaging function completely (I haven’t yet tested them with another messaging capability like Molly/Signal). Also haven’t created cyst for STT to find contact for phone call, etc. Until I resolve these I haven’t tried with any other AA functions, as if it can’t do maps & messaging its no use regardless.
Note they also do not show as the digital assistant when installed.
See my latest couple of posts here describing where I am at with testing AA, voice assistant, etc, this last week in more detail: