the libgwsnmp.so module is compiled for 32bit only. So it is sadly enough not possible to run this module on x86_64.
There is a small "maybe" (read "I don't have a clue" ;-) ) that if you recompile net-snmp as 32 bit that you could be able to load the 32 bit libgwsnmp.so module in there. But.... i doubt it :P
some info: www.cyberciti.biz/.../compile-32bit-application-using-gcc-64-bit-linux.html
My advice, GroupWise is not 64 bit either, so if you do not run any other (64 bit) services on that server, go for the 32 bit SLES10sp2 installation.