jwulbert - First off, I want to apologize for the delayed response. We were just notified of this question. I've been communicating with Houzz to resolve this issue.

I'm looking into your question. I'll post here with my findings.

I checked with the manufacturer. Their response:

We do NOT recommend using
the adhesive mounting on stucco. ALL adhesives need something smooth to
grab to. They may stick to stucco for a short while, however will loose
their grip, as only some of the adhesive surface is actually clinging to the
top points of the stucco. We recommend our stand-off mounting, which does
require drilling into the surface. Another option - use silicone caulk on
each number to adhere the number to the stucco. But you do not want to
make a mess of that, as the silicone will not come off the stucco without
making marks!