Thanks for the response. I did email DH Support… they’re quite responsive, I might add, especially to someone who’s not even a paying customer. =)
They said that rDNS would not be enabled due to server load concerns, which is understandable since running rDNS for every Apache access could eat up resources… and the option is available in Analog so it’s not really a deal-breaker, thankfully.
(Mark, adding the HostnameLookups wouldn’t work, as you found out, because it is not valid in the .htaccess context; HostnameLookups is valid only in the server, virtual server, and directory contexts.)
DH Support also confirmed that if I were to use a unique IP, rDNS on that IP would properly resolve to my domain, and without me having to set up any PTR records either. =)
So all is well.