While I don't question the experience of your friend, I would be cautious about drawing global conclusions on the basis of such annecdotal evidence concerning the extent to which racism permeates unions. Racism permeates every facet of this society, unions included. But unions are no more susceptible (I suspect less) than most college campuses, non-union workplaces, and other institutions, including non-profits.
As for your friend's description of Union Summer and the preoccupations of its participants -- I don't know how old you are, but try to remember when you were 18-25 (the age of typical Union Summer participants). Can you honestly say there was not a day that went by when your hormones were not raging, sending your libido messages intended for another part of your anatomy than your union consciousness. I'd be damned shocked if you put a bunch of 20-somethings together an no one tried to hit on others in the group (although I confess to having met some REVOLUTIONARIES who were so doctrinaire that I would have a hard time imagining them doing anything with their free time other than studying some obscure section of the collected works of Lenin, Trotsky, Mao, etc.).
CWA, SEIU and a number of other unions have very active gay/lesbian caucuses (both formal and informal), and at least in the larger urban settings, there is a conscious effort to promote gender preference tolerance. When you move outside the urban centers, however, I suspect that in most unions, like most other institutions, social tolerance becomes more restricted.
In solidarity, Michael E.