I've seen one nuke and 1 stealth bomber in the matches I've played so far (current level is somewhere in the mid-30s)
Honestly, I've played 2 evenings where there was a 'little stabby cnut' running around and I quit out of the lobby if I saw he was going to continue into the next match. It stops being funny after about 10 seconds. Striker to the head soon sorts them out though, but only when you can see them coming towards you, since most of the time they stab you in the back.
I tend to run around all the time in team-deathmatch. I get shot a lot (it's rare for my kills to exceed my deaths
), blown up a lot, stabbed a lot, but it's bloody entertaining