Yes — trailer work is a big share of roadside calls. Lighting and wiring faults (the #1 inspection item), gladhands and air lines, brake chambers and slack adjusters, landing gear that won’t crank, roll-up door repairs, and mudflap/light-bar damage are all standard mobile jobs. Structural repairs and floor replacement need a trailer shop, but the stuff that gets you a violation or strands a load usually doesn’t.
Trailers break simpler than tractors but strand you just as thoroughly — a trailer with no lights after dark is done for the night, and one failed gladhand seal immobilizes the whole combination. Mobile mechanics clear these constantly: chasing a ground fault through a harness, replacing a seven-way, swapping chambers, un-jamming landing gear (usually a failed crossshaft or gearbox, replaceable on-site), and getting a roll-up door back on its track well enough to close and seal.
The dividing line is structure. Cracked crossmembers, kingpin problems, floor and wall damage, and frame work belong in a trailer shop with fixturing. What a roadside call gives you there is a competent assessment of whether the trailer can legally and safely move to one.
For dropped-trailer situations — you are hooking to a trailer in a yard and find it unroadworthy — the same dispatch works: describe the defects, get bids, and have it made legal before you leave, which beats discovering the problems at a scale house.