Tim,
The 125 is a narrow frame tractor with a quick attach, which should let you use either the old style CC or QA series snow blowers. I would evaluate it like like any other Cub, but the narrow frame Hydros can be a pain if you need to work on the drive train or hydro linkage, unless you can pick up the whole tractor. You'll need strong arms to lift a blower though, as 125s generally didn't have lifts. Nonetheless, a 125 hydro is better suited to snow blower duty than a gear drive, as you often have to inch your way along through drifts and snow banks. You'll be riding the clutch constantly with a gear drive Cub.
The usual condition checks apply, look for unusual engine noises or smoke, test the hydro thoroughly, and make sure the PTO is working and adjusted properly. From hard experience I have found that running a snow blower puts a lot of strain on the PTO, drive belt, front axle spindles, and wheel bearings, so make sure they are in good shape. A hard working snow blower will also take all the power you can give it, an engine on its last legs is liable not to start in very cold weather, or break down under extended full throttle operation.
Another tip if you are going to use it for snow blower duty is to run narrow tires on the front. The wide flotation tires used for cutting grass tend to float on top of snow and give you little directional control. I purchased a set of narrow rims for my 129 and put Tri-Ribs on them, and change back over to turf tires in the spring when I mow.