I don't think it's needed, I have it because it wasn't being used.. If you just do what Cheryl said and spray your enclosure with water you will be fine...
A fogger isn't necessary for Hermann's or any other Testudo species. But there does need to be some way to maintain an ambient air humdity of 50-65% within the enclosure. If that's what the fogger is doing and it's working well then I'd use it. But I would make sure that it is not raising humidity too high or creating excessive dampness.