I would like to speak to the question if they'd work in game or not. Aside from looking awfully high quality, for a generally low quality job (a tool in a mini person's hand) I see no reason why they can't go in as objects. Now I could be mistaken, and they could be very low poly, which would make importing no problem at all, but I digress
As for the issue with them working, each one brings up questions of its own:
Pepper Spray could work with an added command, and possibly a new particle too, you activate it on a person, then they get stunned for a short period of time. I see no reason why this couldn't work with the proper scripting. The worst part I would imagine would be making a new animation should there not be one that works already.
Nightstick: Again, fairly easy, and potentially one of the easiest addons in the game. I would imagine it'd work as a weapon to beat people down faster. You'd just simply write this as a script like the others, where the officer gets it, then he/she has it and can take someone out in 3 seconds instead of 5, while getting the same damage. I'd imagine this would be relatively easy. I haven't adjusted fight damage before, so I am merely guessing, but I'd imagine that's what would happen. Now if that wouldn't work, you could also make it so that it would increase protection from fight damage. The fights would last longer, but you'd get less hurt. I do believe there is a setting for that in the game, but I don't know if that can be changed by script, or if it has to be done through model switching. Worst case scenario, it's just something that looks cool
Grenade: I think there was already a discussion about this, and that it's possible to make work.
Tazer: Similar to the above, I can't remember how, but I think Hoppah explained it
Flashlight: Easiest ever. Make them hold the new equipment, and while they do, it activates a person light. The get script would just have them pull it off their person, and the light would come on. This would be no problem to add. I think I did it once with a gun model (I was lazy and didn't wanna make a flashlight for testing purposes)