There are only a few areas in the campaign that truly prevent you from using the mechanics (which are varied enough to have pros and cons depending on both the layout and enemy); they may at most ask you to adjust how you use them. I would say it is actually the enemies that are a bigger factor (with level design merely adjusting that effect - providing cover, forcing you to avoid charging enemies in other ways).
For example, the indoor market of Chris 1 (IIRC the most narrow area of that chapter) isn't so narrow that you can't make use of the dodging to go prone, particularly when dodging backwards or at an intersection. I would say the spider J'avo enemies are a bigger factor, encouraging you to use counters. Even in cramp scenarios, consider the vertical aspect of sliding or dodging to the ground: this will make you mostly safe from horizontal attacks of knife-wielding J'avo until they adjust a moment later (ideally, you set up a headshot stun or outright kill the enemy before getting up). And most areas in the game are not narrow hallways like the indoor market.
I would say 90 to 95% of the time where you are given full control of your character, any and all skills used in The Mercenaries are applicable to the campaign - it's fundamentally the same combat with some pros and cons (harder difficulties, more variety vs. tension of time limits). There are moments like the ice hill, projectile heavy areas with little cover (as in stuff to get in the way shooting, not barrier to use the cover system with), and some bosses where that may not be the case, but not enough to damn the game's use of its own combat system.
Pro and No Hope while possible to beat on a first playthrough, really are made with a second playthrough in mind with some skills.
No Hope means no skills. The real difference maker are weapons (and, of course, experience with enemies, but you may be able to simulate that with Mercs). Honestly, only Leon's campaign really hurts without later weapons; the starting weapons are pretty much atrocious and the characters feel weaker than others until you pick up the Assault Rifle. You can do No Hope on a new playthrough, but expect a challenge unless you cheese it in some fashion. If you know your stuff and this is your second playthrough, I wouldn't recommend against it.
Professional is definitely doable on the first playthrough. In fact, if you play other TPS (Uncharted, Last of Us, Vanquish, Evil Within etc.) on higher difficulties you really have no business playing anything short of Professional. "Normal" difficulty is tragically easy and "Hard" is not much better. I don't think you need much skill progress with Pro, but you may want to be smart about your choices and not waste skill points on trivial stuff. Damage+ is nice for Leon for the reason I mentioned above. Unless they nerfed it, going solo with some NPC skills can trivialize a lot of the game.
I'm completely unaware if they made any big changes with this version. cvxfreak said the enemies felt easier to kill, but I doubt that.
