Yes. I've had a small webapp running under it quite happily (complete overkill, but it's a personal project and I was curious).

Very basic hello world app hosted under gunicorn (just returning the string "hello world", so hopefully this is measuring the framework time). Siege set to do 10k requests, 25 concurrency, running that twice so that they each have a chance to "warm up", the second round (warmed up) results give me:

    pypy   : 8127.44 trans/sec
    cpython: 4512.64 trans/sec

Yes, have been using Flask on PyPy3 for years. I get about a 4x speedup.

I just tested it and it works perfectly.