I googled sugar tip and reports are it is sterile. Only found one reference in a brief search for Showtime. Did not mention if it is sterile.

You didn't ask, but The Chiffon Series is reportedly sterile. Blue Chiffon is lovely and I've never found a seedling.

Minerva (and greek series) is supposed to be sterile, but there are mixed reports on others besides Minerva.

Thank you, Marie!

For anyone wondering this discussion is apparently about Hibiscus syriacus cultivars.