The hardwood floor is the same temp. as anything else in the room, unless you have a slab construction, cooler basement (if this floor is the 1st floor) or you have a very large spread in the on/off (upper/lower limits) cycle on your heating system. Also the location of the tank to walls, i.e. interior vs exterior. exterior wall will have more influence then interior, etc.
Condensation is relevant to factors such as ambient temperature/humidity of room. outside conditions, dry, cold as well as the swings between your room humidity/temp. and the tank humidity/temperature.
I believe you can actually get condensation on your tank and Not have a high humidity condition in the tank persay. It will be higher then the room or the condesation will on the out side of the glass, if the tank temp. is lower then the room. The plants are the better gauge IMO, then the glass, however, I think it would be high enough that the frogs would be fine.
Plastic, such as poly. will give the tank a "thermal break" from the wood (the same principle used in vinyl claded windows, such as Andersons). Also, any insulation foam will also do a similiar thing. If your tank has a plastic frame, do not use styrofoam directly against it for any long time, as you may get "migration" of the polymers from the ABS to the foam.