Hello,
I don't know if SCOM is that bothered about .3 but I'm pretty sure it needs .1.3.6.1.2.1.1.1, .1.3.6.1.2.1.1.2, .1.3.6.1.2.1.1.4, .1.3.6.1.2.1.1.5 and .1.3.6.1.2.1.1.6 (I'm getting .1, .2 and .5). It could well be the case that the lack of .3 is a problem too, but certainly .4 and .6 are a showstopper.
Indeed, as you say SNMP is enabled and the query is direct from one of the SCOM management servers to the devices.
Cheers
Steve