If firespray are patrol craft for local enforcement, I'm actually more than happy to paint up a few 'black-and-whites' for intersystem ships. The Aggressor does feel like a strictly contract ship (not necessarily bounty hunter, but a mercenary sort).
There might be some interesting pseudo-justifications in having some of these other craft around as localized reinforcements adherent to the Imperial authorities or otherwise in the Imperial employ beyond just simple bounty hunters. Naturally, it's also just good branding mixing in some lesser known craft with the iconic frames.
I'll admit, I'm having a hard time reconciling the generic YV-666 and Jumpmaster 5000 with non-bounty hunter use. It's not impossible, Jumpmaster's were superb long range ships apparently, but the YV-666 is still a light freighter so... yeah. Imperial convoy guard things? Of course, I'd much rather see ATR's for YV-666's, Escort Shuttles for Jumpmasters, etc, but I'll live with it.