Dnsmasq 'address=' function is just a substr() call, which is as fast as 'normal' hostname blocking (host == "adhost.com"). No regex magic is required there.

You are not able to block something like 'ads.%.adhost.com', but only (prepending wildcard) '%.ads.adhost.com', which in practice will cover almost all scenarios where random subdomains are used by adhosts.