I’m missing your point.
Have a “don’t ask, don’t tell” policy?
If you’re paying a good lawyer to save your ass from being sued to perdition then it’s their job to answer these questions for you.
Under some legal systems (the British one for instance) there’s a pretty simple rule of thumb which I think applies just as well States-side: if you fire an employee for conduct/misconduct, then ask yourself if the specific grounds for the specific instance of dismissal, amount to any or all of the following:
1. unlawful activity (e.g. committing a criminal offense)
2. explicitly against company policy (e.g. tardiness)
3. directly bad for business (e.g. being rude to customers)
4. bringing you into disrepute (e.g. shoddy workmanship)
5. disrupting the work environment (e.g. drunk, abusive)
If you cannot satisfy a single one of those general ideas then you really do need to check with your legal advisers that the specific reasons for firing the employee, aren’t a lawsuit waiting to happen.
Where it gets difficult for me to give a confident answer, is if the only reason you even suspect that an employee who earns his keep and does his job well, is homosexual, is because of an accusation from a colleague. Absent any explicit evidence that it’s affected their ability to do the job you pay them to do, it wouldn’t do you any harm to consider the possibility that the motives of the “whistle blower” may not be entirely innocent and their “evidence” might be gilding the lily.