I think the only problem with this, is that the fact that Zone's mainly a PvP server, and that adding creatures/active npcs of any sort into the mix somewhere would cause a bit of a disturbance. I don't think that it's a bad idea, it's just that it would require a lot of work in several areas, especially scripting. Although, I do suppose we could edit the bot scripts a bit, and maybe get something out of that? It would still be harder than that, though, as the currect bot functions aren't all that great.
(For example, they can't even shoot diagnolly. 
)
Besides causing a lot of work, zone would become more like the other servers where people would rather kill monsters than specialize in PvP. There are many pros and cons to it, but I think that this could indeed have more pros. I guess its not quite the same as slashing idlly at a walking potato as when you're shooting up hostile alien beasts with big, futuristic guns on a desolate planet.
No, it's not the same, due to the fact that you cannot eat an alien with a hard carapace, as you can a walking potato.
(Eww, raw potato. 
)
Oh, and another thing, forgot to add. I think the creatures shouldn't have the same weapons that we do, except if they're very advanced humanoids or something. They should have melee attacks or natural ranged attacks, like a mandible grab & toss or head-on charge, or a barbed venom spike that would launch off the tail of a scorpid creature of sorts.