Hi Deep, which software version are you using or do you intend to use? generally we would recommend you to use the latest buildroot, follow this to build a typical target http://docs.blackfin.uclinux.org/doku.php?id=buildroot:build-system:build_a_target.
In make menuconfig -> target packages -> networking applications, enable the item "netsnmp". However as snmp is not in our test/feature list, you may have problems compile this on the no-mmu Blackfin CPU. Take a look at this for the application difference without MMU, http://docs.blackfin.uclinux.org/doku.php?id=porting_applications. To make it simple, in most cases you need to replace the fork according to this link. The source code would be located in somewhere like output/build/netsnmp-5.7.2 after building, one option is to change the code there. Let us know if you have further problem during action.