No mention has ever been made of armoured vehicles, it could well be that they are simply not used in an environment where the armour and shielding on a small vehicle may be of little use against the weapons of a starship in orbit.
Well nor the battle to strong refers to hoppers.
May be some sort of transport/combat vessel?
As for marines I always thought of it like this:
Starfleet security act as marines in the traditional role of marines (NOT the US modern Marine version) as guarding the ships/stations and limited on shore operations.
And you also have full battalions like shown in DS9 (possibly MACOS) that speclise in all the ground combat dutys. Nor the battle to strong refers to units of squad and platoon size so it seems they have a tradition like army structure, though we have limit information on Ranks. Though a Colonel in undiscorved country did appear, yes he had a admiral uniform but to be honnest uniforms in that film were a mess!