First thing is very miss leading you will need more files then just your act.dat backed up from an activated vita
you need:
vd0_registry/system.dreg
vd0_registry/system.ireg
tm0_npdrm/act.dat
so backup these files from an activated vita and you are covered to do a complete restore of your vita
yes this works for a banned psn account
and no if you dont have a copy of these files then you are outta luck on getting your psn account back up and running on your vita without a ps3 (if your psn account is banned and you dont have a backup of these files from your activated vita you cant activate your vita theres just no way ive spent hours and hours trying to use vita-activator and just my act.dat file alone you need these other two files as well)
https://www.youtube.com/watch?v=wBzpHaXxuLE