Can Printer Sharing and Popups be used between Macs?

No, it cannot.

The Pharos server expects a direct connection from the client printing the job.  If and when a sub-client who is piggy-backing off of a properly connected client prints, the correctly connected host Mac will get the Popup rather than the shared sub-client.

So if Mac A connects to the server properly and shares the printer, and Mac B connects to that share and prints, Mac A will get the Popup rather than Mac B, and the job will fail unless Mac A completes the Popup request.  Furthermore, if Mac A doesn't know Mac B has connected to Mac A's share, Mac A will get seemingly random Popups.