suction cup base dildoes

There are many different kinds of harnesses out there. Yes there are some that are compatible with suction cup dildos. Be sure that your suction cup is sturdy enough to support the weight of the dildo when horizontal. Take some measurements of your dildo and look for a o ring type harness that will fit snug just below the balls and just above the suction cup. They are definitly out there.

sure they can...

Sure they can. Just use your inner Macgyver and rig it up

Sure they can

with most, sure.