Is a mobile home loan that is secured by the title to a mobile home, but not the real estate it is attached to subject to HPML? I can't tell if the mobile home is just exempt from HPML Appraisal requirements or everything?

If the mobile home is the consumer's primary residence, it's subject to HPML, whether you have dirt or no dirt. They are exempt from the appraisal requirements within 1026.35 though, as you say.

Just to add: effectively, the appraisal exemption stuff will only cover the need for a certified appraisal (if not otherwise required under the Interagency Guidelines), extra appraisal on a flip, etc. if the loan is secured by a first lien on a dwelling, since the Reg. B appraisal rules don't have an exemption for mobile homes for the notice and delivery requirements.