To my knowledge, BSM does not accept any SNMP alerts directly. Those have to be handled by an SNMP app like HP NNMi or the HP Integration Adapter. NNMi can query and trap snmp v3. The integration adapter does not query, but can handle any trap.
Regarding the Platform Administration guide for BSM 9.21:
“BSM uses SNMP version 1.0” and still does not support SNMP version 3.
There is already opened ER for supporting SNMP v3 but it is currently in deferred status. This means that at this stage it is not included as supported in either of BSM versions but will be reviewed for including it for the future releases.