Yes, you need the Solaris network transition kit available from Sun. A number of those have been made available over time:
1) NSkit 1.0. A version of SunOS 4.x NIS executables made to
work on Solaris 2.x. Fully included in patch 101363-08.
2) NSkit 1.1. Native, available from OPcom, but never left beta
stage. Didn't do DNS lookups well (the entire server hangs until
a DNS request is answered).
3) NSkit 1.2. Native. Freely available from the Solaris 2.x
migration initiative home page. Supports multi-homed hosts,
async DNS lookups and shadow password maps. Also shipped with
the 2.5 server kit.
NSkit 1.2 is available for SPARC and x86.