Having read all that is said here i'd like to add my 2p worth. I fully believe that the conglomeration of hip-hop and techno is worth doing and can provide a sound that stimulates both sides of the musical brain.
I think the problem comes for most people when both are added together and given enough room to manouvere within their respective genre's techno is a powerful genre that DEMANDS space to perform it's function, likewise Hip-Hop/RAP also demands exactly that same.
I have had a go at creating a track that covers both bases, i know its a shameless plug, but iot really do think its an illustration of this argument. You may like the track, you may not.
www.theinspectors.co.uk then go to the player at the top and select the track "No threat" this is me vs jay-z. its more of a bootleg than owt really, but i think it works.