Not sure what/how they winterized your unit but understand if you have antifreeze in the system and the water heater bypassed, by hooking up to city water, you will flush the antifreeze out of your plumbing and not have hot water. (because the water heater is bypassed).
If you are OK with with this scenario, then just hook up to city water and as mentioned, the check valves 'should' keep any water from entering the fresh water tank. I say 'should' because sometimes they do stick open and fill/add water to the fresh water tank when it really shouldn't. I would crack the fresh water drain when I got home just to be sure no water did get in there by accident.
Once you return home and if you again need winter protection, you will need to re-add antifreeze. (if that's what they did to winterize in the beginning)
Also, some places that winterize units remove the water filter housing (if so equipped) and leave it off. Make sure yours is in place or you will have water inside everywhere once you hook up to city water!
2016 Flagstaff 8529IKBS Diamond Package 5th Wheel
Ford F-Series SCREW 4x4
TST Tire Monitor - Sinemate 3500w Gen.
2016 Nights Camped = 42