I would definitely recommend using the correct 2 part adhesive, and only consider anything else as a temporary measure.
I would also avoid having anything protruding from the bottom of the transom (eg screws and washers) as this may affect the smooth flow of water and cause cavitation when planing. I have found that inflatables are much more affected by this than hard hull boats.
On the other hand, if you are just making a quick repair so you can sell your inflatable and buy a RIB then it's only your conscience that you have to worry about
John