Will genital herpes cause buttock ache/ back of leg ache even though rash is elsewhere? i.e penis

Probably not, but...: This depends on the nature and timing of the pain. If the buttock/leg discomfort is only during a genital herpes outbreak, or starts 1-2 days before, and if it clears up in another 1-2 days, they may be linked. However, herpes doesn't cause chronic or persistent, ongoing, deeper back, buttock or leg pain, that doesn't accompany outbreaks. In that case, it's an entirely separate problem.