Unix nagios account : audit requires it to have password expiry : how to work around it?

We got an audit finding that our Solaris (& possibly Linux as well but I haven't
verify) OS account used for Nagios monitoring do not have password expiry.

Q1:
However, when a Solaris account got expired, it'll cause service disruption
(just like root's cron jobs): is there any way around this?

Q2:
Can we set the SHELL for the nagios account to   /bin/false or no shell so
that it's deemed as non-interactive account & don't require password
expiry?   Will Nagios still work with no shell or a false shell??

Q3:
if we change the password of this nagios account periodically, do we
need to change it in nagios (script or settings) somewhere?