What are the default versions of SNMP that are supported in OpsCenter?

SNMPv1, SNMPv2c, and SNMPv3.

What is SNMPv2c? How it is different from SNMPv2?

Is the OpsCenter SNMP community name configurable?

Yes.

See Configuring the SNMP trap community name for OpsCenter.

How is the OpsCenter community related to the public community?

Is the default community name of "OpsCenter" just a name for the community, but still considered public because of certain attributes?

The "OpsCenter" community used by OpsCenter is public, but the community name is maintained as "OpsCenter".

Generally, the "default read community string" for the public community is "public". Public community means read-only access to SNMP traps.