I believe this is classed as 'positive discrimination'; there are several publishers listed on Duotrope who do this: only women, only disabled people, only children, only Americans and Canadians, only native Americans, on.
As a writer who considers herself of no specific demographic other than being from the UK it can actually be frustrating to see barriers like this where you have no control.
Surely it's better to cast your nets wide and say you take a particular interest in works by LGBT than to close off whole legions of potential writers. But anyhow, your call.
One thing... and perhaps I am naive to these things, but until I read Ethan's reponse I didn't know what LGBT stood for. I guess if you fall into the right categroy for submissions you'll get it. But don't be surprised if you get submission from people who are straight, who like me didn't know what it meant. It's always best to spell stuff out when advertising in an open market.
However good luck with you publication. I love the name, by the way.