Hello,
User name starting numeric charactors or user name that is consist of all numeric charactors should be supported in NX-OS 5.0.x.
There is a bug asking support for numeric user names for SAN OS and SAN OS based system (NX-OS)
that is fixed in 5.0(1) 4.2(4) 4.2(3) 4.2(3.6) 5.0(0.166) 4.2(1)N1(1).
CSCta00308 All numeric user names support in SAN OS
Regards,
Kimihito.