I cannot speak for moxie or Signal. I can speak for my own experiences, as the maintainer of a fork of signal-cli, and I have never seen any evidence that Signal's servers block signal-cli or my fork. I don't know about signal-cli but my fork clearly identifies itself in the user agent (and another field called the "signal agent") to the server. If they wanted to block me they could.
I cannot speak for moxie or Signal. I can speak for my own experiences, as the maintainer of a fork of signal-cli, and I have never seen any evidence that Signal's servers block signal-cli or my fork. I don't know about signal-cli but my fork clearly identifies itself in the user agent (and another field called the "signal agent") to the server. If they wanted to block me they could.
edit: signal-cli also sets a user agent clearly identifies itself: https://github.com/AsamK/signal-cli/blob/05abb3f9f6294677d2d...