Hello,
I think this is good approach - I would certainly recommend to keep <sid>adm user as it is and to not mess with it and rather create new user and make is as similar as possible (same groups, environment variables, etc...)
As far as I know there is no official way how to change this user or how to specify different name during installation and from past (non-HANA) experience I know that some features might be hard-coded against this user..
Tomas