If they are using standard compliant tools like pyenv, venv and pip then uv will play nicely with that. In fact I'm working on a project like that right now. The 'official' guidelines says to use pip and venv, but I'm using uv and no one else notices.

If on the other hand they're using a more optionated tool like poetry then it won't work as well, but that has more to do with poetry doing its own thing and not playing nice with other tools.

Yep. You can gradually start to use feature set of uv. Beside it uses standards of python project management, so you don’t have vendor lock-in here.