i am not a SCOM expert but it´s right, in SCOM there is no host up Event. SCOM is closing the host down Event. Maybe it´s possible do send a msend when SCOM is changing the state of an Event. If you need an OK Event in BEM you can write a rule changing the severity to OK for the host down Event.
We are using the "Seamless SCOM to BEM" Solution. When SCOM is closing an Event the Event is also closed in BEM.