Generally speaking, I have had great experiences using ports-mgmt/synth over the years, daily (with very rare exceptions). It handles a whole bunch of things that I had previously been doing manually. While I can't say that I've literally never had a problem with it, I can say that they've been infrequent, almost never the fault of Synth itself, and it's been waaaaaaaaaaaaaaaaaaaay easier and waaaaaaaaaaaaaaaaaay less problematic for me than handling it all manually. But specifically, with regards to the "But the server is a production server": It builds everything (either on a remote machine or on the target machine itself) in a jail and then makes the built packages available for (e.g.) "pkg upgrade".
I'll also say that many people use ports-mgmt/poudriere for (I gather) the same reasons. I have zero experience with, and almost zero specific knowledge of, Poudriere (mostly simply because I've been so happy with Synth), but people seem to generally be happy with it, as far as I've seen. So you may want to look into one or both of them.
