Was Googling this today and couldn’t find an answer. Wrote support. They don’t support it.

Does Dreamhost support mod_ssl and SSLVerifyClient? I tried putting the following in my .htaccess at singpolyma.net/catest, but nothing happened

Sorry, but I’m afraid not! While we do have mod_ssl, there is no
SSLVerifyClient. Sorry about any trouble this causes you!

If you have any other questions, just let me know!