Will using these rads again likely cause any harm to any part of my
system? (It uses a combi boiler.)

Is there a reason not to buy new ones? Radiators aren't particularly
expensive. Not as expensive as replacing a combi boiler that has just
decided to fill up with sludge from an old radiator, anyway.

In any case, you'll need to examine the radiators to determine their
condition. They might be just fine if stored correctly. (i.e. not in a heap
in the back garden).

Christian.