Please try the Rebuild Topology button from the nworks UI.
This is available on the Management Center tab, at both the Management Center level and by selecting each Collector under the Management Center node.
This will force a rebuild of the whole topology as seen in SCOM.
This discovery of new Hosts should be automatic, but it is possible it was missed for some reason (for example, if the SCOM agent was offline when our Collector threw the original Rebuild Topology event)
Let me know if that helps!
Vice President, Product Management