This is the real story. This is 100% a problem with Radix. Safe browsing targets the website not the domain. No reason a registrar should be suspending an entire account over something a company reports. Black-holing the A and CNAMEs on a subdomain? Maybe..... But even then I don't think it's the registrars place to do that. Freezing the entire account? Absolutely not.
Google allows you to use TXT to verify though, since this "feature" of disabling domains because of Safe Search is based only on web contents (A/AAAA/CNAME) they could disable those and allow TXT anyway since those are AFAIK harmless