Hey Ron @wpmuguru thanks for the reply.
Understandable that it doesn't work with the domain mapping plugin out of the box (Again I think it's probably due to that /blog I am appending to the "domain". But it seems like it would potentially be possible with domain mapping along w/ an updated .htaccess file?
Possibly adding /blog based on http_host within rewrite conditional? I don't think I can do a conditional RewriteBase
Any shove in the right direction would be greatly appreciated.