Some pedals are designed to be disposable, with sealed bearings as you mentioned. Usually these have a plastic dust cap (the cap you referred to) which is not easy to remove. If this is the case, you won't be able to do anything with the pedal, even if you get the cap off.
Typically, as you seem to know, if a pedal is designed to be serviceable, there will be some obvious way to remove the dust caps (i.e. wrench flats, special tool socket, etc.). The lack of any such feature makes me think that they aren't serviceable and likely have sealed bearings.
No guarantees, as I have never taken the cap off of one of these pedals to find out, but I don't think you can outright ruin the pedal just by taking the dust cap off. If the pedal is already not turning freely, then I don't see any harm in taking a look.
I see two possible outcomes:
Pedal has sealed bearings and will need to be replaced soon anyway, regardless of whether you damage it further by removing the dust cap.
Pedal has loose bearings, so you can clean and re-grease the parts, then put it back together.
In either case, you should be able to just pop the dust cap back on afterwards.