It's been a long time since I had to set up a printer - last two shops I worked at used Microsoft for printers.
How do you print to the printers from VMS? Are they set up in DNS at all? If I remember, there was a UCX (or UXC?) utility on VMS to work across to UNIX. Let you learn UNIX while on a VMS system. That might help get you up to speed. It may also allow you to print from Solaris to VMS to the printer. Check the documentation
(a quick search found this)
But to really answer your question - yes, the IP has to be somewhere - if not in NIS, DNS, NIS+, then the hosts file (althougth I still think UCX has a way of sharing the printers with UNIX boxes - you might only have to set up the printer locally on Solaris to point to your VMS servers).
And it seems since you have something that works....
"If it's not broke, don't fix it!"