I do believe you can have a roleplay server with the same community as those on Perp, however, I highly doubt the quality will be anywhere near as good as what's been delivered on GMOD, this is partially due to the mechanics that's already been established on the GMOD server, the main mechanic being seamless interiors with the open-world, giving newer players a sense of security and safety should they be new to the server, most GTA servers (especially the larger ones) force you to do illegal money-making methods in open public areas to which most players normally get robbed as soon as they're finished as larger groups tend to 'camp' outside these zones to steal the loot from the tedious processing methods most servers have.
Government jobs would also require a bit of reworking to fit around the GTA playstyle, being a police officer on FiveM can be a nightmare but it's manageable once you have knowledge of the map, and keep communication crystal clear (not sure if this is still the case with the PLPD), but the sheer size of the map can make this difficult, the same would apply for medics as well, and if you've played any medium to large FiveM server, you'll know just how demanding being a medic is, which I can imagine will be stressful considering how short-handed it is on the server already. I've done some work on blip mods to make this easier for government jobs, however, it doesn't remove how demanding the jobs will become.
What makes GMOD unique is the customization players are provided with tools such as the physics gun, temporary stores, and residencies that can be bought in-game, and other options that let you manipulate the environment, all of this is virtually removed on all FiveM servers and is extremely difficult to implement. Now if you're more of a shooter the benefits are most certainly there for you, you're given more opportunity to do activities such as mugging, house robberies (which I've made a new mod for), kidnapping and bank robberies, newer players also don't need to rely on skill trees for accuracy or damage either making combat a tad fairer. Combat on GTA in general is a lot more varied, of course, and this can benefit both newer players and old.
TL;DR: The benefits sway heavily towards combat, rather than roleplay, calling it Perp would only be relevant because the player base would mostly come from people who have played on this server. It's an interesting concept and I do feel like it's worth a try however, if anyone's willing to invest into it.
