See URL for upstream bug Attaching patch to properly limit to 32 bits. May affect other arches, only tested on sparc.
Created attachment 97003 [details, diff] Patch to fix 64 bit counters
Specific ebuild patched against is net-snmp-5.2.1.2-r1.ebuild
After a couple weeks of no activity, I've added this patch to 5.2.1.2-r1 to apply to ARCH=sparc myself.