While I don't think I'm evolved enough to be totally okay with knowing someone has a second full-time job... if someone working for me is delivering the goods and nice to work with and I don't have any idea, in the abstract I think I don't have a problem with it.
I am hiring for results, not keeping a chair warm.
Honestly, I usually do 90% of the most important creative work for a given week in a few hours. Always in a concentrated burst that I can't predict ahead of time.
Allowing my brain to stop feeling guilty for that is likely going to be a life-long challenge, but it doesn't change the reality of it.