I'm quite certain that the terms & conditions of the rate plan don't specify that a specific sexual orientation is required to be eligible for the rate.
And I'm also certain that the rate plan doesn't say anything about two people sharing a room are required to be of the same sex.
The only issue would be if a rate plan was sent to specific members of Starwood Preferred Guest, and it specified that only those members who received it directly would be eligible for the rate plan.
I don't think this is the case, and I doubt it would be a problem at checkin in any case.
You shouldn't have anything to worry about.
Besides, it would sure be fun to be denied the rate with the explanation that you aren't G/L/B. What a great story that would make, I guarantee you could make more on it than you'd be out in incremental room cost.
