Yup, I imagined him as a stealthy fucker who can put up sentry guns for defense and as distraction, while closing on enemy from the shadows. More about tactics than force, ambushes and that kind of stuff so a blade in the gun can prove to be useful.
That's not very realistic, because a bayonet is not suitable for any stealth action as stabbing someone results in loud screaming. It's more something I'd expect an assault trooper has for storming although realistically it's more of a historical, antiqued weapon that isn't used in modern combat at all.
I agree that the bayonet is more suitable for the assault soldier but disagree that it's an outdated thing. Soldiers are still trained with their use in today's militaries, and in the future knives (and bayonets) will have the possibility of being enhanced through technology (ie: armor piercing laser sword.) Also, your tactical guy would more than likely sneak up behind someone and slit their throat rather than charge them with a bayonet.