Because it may have escaped your notice,
HP have already ported Nagios (partially, one should add) recently.
It's now available in their Internet Express collection of OpenSource software.
http://h20293.www2.hp.com/portal/swdepot/displayProductInfo.do?productNumber=HPUXIEXP1111But compiling your own nagios and plug-ins is of course preferable.
Besides, if your nagios server doesn't run any SNMP checks (or check_ifoperstatus) then there's no need to have net-snmp or Net::SNMP installed.
These are only required for the SNMP related Nagios plug-ins.
Madness, thy name is system administration