Please only answer if you know, no speculation please.

The descriptions say the perks apply only to standard frags, but since the weapon attachment takes the place of the frags, but technically is still a "grenade launcher" I'm unsure as to whether these perks apply, I believe yes, but if someone knows and could tell me, that would make things simpler.

If you are referring to the underslung gernad launcher, than yes the perks affect that as well because it uses your frag grenades

Good good, thanks for confirmation!

Do the 2 skills affect other classes or only soldier class?

Just soldier