Hi Albert,
I don't know for sure. They are very attractive to insects so there is a pretty far isolation distance need to ensure no crossing when saving seeds. But some plants that have perfect flowers are still attractive to insects.
Hand pollination won't hurt anything so you can do it if you like. I recommend the morning hours before it gets too warm.
Remy

Thanks. I went out this morning and there was one lone wasp and a few tiny insects. I rather suspect it doesn't take much. Another mystery is how did I come by these hollyhocks. I have never purchased any hollyhocks. A landscaper gave me a handful of short, very dark maroon, almost black, doubles which germinated very poorly. The pink ones must have been in those seed. They are about 6-7 feet tall and have single flowers about 4 or 5 inches in diameter. Pink with darker centers.

Most or all of the hollyhocks, even the peony-type/doubles, have come back true-to-type. The singles are less top heavy, though, so don't fall over as much as the peony/double type.