subdomain and domain are considered same by adwords? for seo, they are considered two separate sites as you can have multiple listings. how does adwords read redirects, and how do they treat 301/302 redirects?
adwords follows the redirect whereever it goes, but final destination need to be withing the root. either sub folder or sub domain doesnt really matter what are you trying to accomplish with 301?
as long as your display url and redirected url matches you are not going to have any redirect problem with main domain or subdomain.