Absolutely.
"Headshot Expert", "Brutal Expert" and "Steel Fist Expert" can all be got quickly from the opening scene on the boat.
The hardest one to get during normal play is "Stealth Attacker" as hardly any enemies have their back to you for long enough. In fact I only know of one point where you are guaranteed to get a stealth kill which is one guy in the fortress just after you climb in. I ended up just killing him, dying on purpose and killing him again until I got it.
If you get behind enemies when you're heading toward them, even if they've seen you and shot at you, you can still do the melee attack.