are there any enemies who i wont encounter at all just coz my level will be too low for them to spawn?
No.
the enemies will just have less hp for sure and maybe a reduced weapon loadout but I'm not sure of that.
Eh? I don't believe they have less HP's or weapon loadouts just because you're higher level. They just won't
increase their HP's or weapon loadouts past what they had before the DLC's....in other words, they don't scale with you.
...but I only have 1 of the DLC's so far so not 100% sure on whether they did or did not give enemies another scale-up point if you have them all. Enemies in NV don't scale per se but they do alter/increase possible weapon loadouts at a few certain lvl points since one of the patches, I think. Can't remember exactly, it's all getting foggy now.