My In-home daycare used her husband as an assistant. He was checked out by the city and was a very nice man. I wasn't crazy about the idea for the same reasons as you, but as it turned out, he was great with the kids. A bit less motivation than the wife, but he was good. No diaper rash from sitting in wet diapers, kids were clean, home was clean, and no emotional problems from the little one.
I must admit, if it were a man that I interviewed to watch my daughter, I probably wouldn't even have met for the interview. Nothing more than my own personal choice.
So meet the male assistant and check references. If you are completely uncomfortable, don't do it. You have to be comfortable with your choice. Look his name up on the web and hers as well. People love to take time to post negative stuff. If you find nothing I would take that as just as good a sign as finding positive posts.