Please post your actual domains... this is no place for general guesswork!
Well, I wouldn't say http://dkg.drupalgardens.com is "redirected". In fact that URL stays put. http://www.davidkennethgroup.info is permanently 301-redirected to http://www.davidkennethgroup.com, and the latter hostname is a CNAME for dkg.drupalgardens.com -- guess that's what you mean, but I like to be precise.
Either way, I think you misunderstand the connection between [a] the domain you use in your SMTP sender (MAIL FROM) and/or message headers (From/Reply-To), call it example.info; and [b] the HTTP presence of http://www.example.info.
While SSL is strongly advised for other reasons, it doesn't matter for deliverability if links in the email body are to http://www.example.info or https://www.example.info. And if you're sending from email@example.com, the recipient's mailserver is never going to check the DMARC policy/DKIM signature/SPF record of example.com. Those are all SMTP-level measures, not web-level. The fact that a web URL redirects to another web URL is irrelevant to SMTP policies (in fact, if it were not irrelevant, such a relationship could and would be abused by spammers).
On the other hand, from the deeper content inspection standpoint, the fact that example.info redirects to example.com and example.com was blacklisted in the past (and therefore may still be on private URI blacklists, though it is not on the public ones as far as I can see) could readily impact deliverability. Frankly, I would stay as far as away from that blacklisted domain as possible until/unless it can be proven that there's another wrinkle that's unrelated to this old (but, essentially, still primary) domain.
And, of course, proper DKIM setup and accurate SPF are vital. SPF isn't necessary w/Marketo unless you sign up for their additional "branded sender" service. But DKIM must be signing correctly if it is enabled: it is far worse to have a broken DKIM signature than to have no signature. Your DKIM record for M1._domainkey.davidkennethgroup.info is broken, so if Marketo is signing your emails, they must be permfailed for broken DKIM. (I can't say whether your Zoho selector was similarly broken because I don't know your client ID over there.)
I think you should work closely with someone who understands the full spectrum of SMTP and HTTP and the measures you've taken so far to rescue your reputation.