Potential employers do not typically monitor hook-up sites like A4A, manhunt, bigmuscle, scruff, grindr, etc. They may be interested in your linkedin, facebook, twitter, and similar social media accounts, but I'm not convinced that they'd expend invaluable resources figuring out your sexual proclivities even if they're curious. If they were truly rigorous, they might look at your public comments (chat room posts, tweets, blogs, etc.), but even that has some limitations. If you're a potential executive-level or C-suite employee, particularly if the company is publicly traded, the level of scrutiny and investigation would be significantly higher because the company's exposure to potential negative publicity would be similarly higher.