How far can you trust the output of the Net-SNMP command line tools? Maybe they are just printing the data in hexdump format because the SNMP OID isn't known a string, or the data doesn't look like a string?

Without knowing anything about SNMP, it seems that at least snmpwalk.pl from the examples will use the snmp_type_ntop function to convert things to something printable. I don't know if the data you receive already is supposed to be the decoded value or maybe is still in ASN.1 format.