What part of FIM do you ask about?
Password reset feature? I think it is supported on Surfaces, but not Surface RT probably (if you are thinking about client - Password Reset site would work there also).
Hello,
since RT is out of scope because you can not install software (beside APPs) on it, all other surfaces are running on "normal" client OS.
In addition to Dominiks post keep in mind that most Surfaces run Win 8.1 which is not currently supported but it will work.
Currently FIM stucks on Win 8 (Client side) and Server 2012 (nonR2) (Server Side).
with FIM i mean FIM 2010 R2 SP1.
Support for current OS releases will be added to MIM 2016 which will be released very soon.