kanye producing does not equal hip hop. kanye as producer just means someone who knows how to use the studio as an instrument.
william orbit produced Electrical Storm and Hands That Built America, and they didn't end up as techno.
Nellee Hooper Produced HMTMKMKM, and it didn't end up Trip Hop
Dr. Dre coproduced one of the tracks from NIN's "The Fragile" and it was anything BUT Hip Hop.
This may be a poor example, but Fiona Apple and Dave Matthews Band have both worked with Hip Hop producers recently (i like fiona, don't care for DMB) but neither one yeilded anything close to a hip hop album.
People have range. Flood produced both The Downward Spiral and POP, two completely different albums. Daniel Lanois produced Willie Nelson and Luscious Jackson. Eno produced Bowie and Talking Heads. Lillywhite worked with Phish.
What is coming out of the more progressive Hip Hop movement (and Kanye is the leader of that pack, It i may be so bold) are people who know how to produce.
?uestlove from the Roots produced Joss Stone's last album, and she cannot be categorized as Hip Hop.
At most, I think we will hear a collaboration in terms of Kanye PRODUCING something for U2, not rapping on it, and it will not be Hip Hop. If anything, it will be more boundary-pushing, along the lines of Zooropa or Pop.