I'm not sure on this one. Best way to find out would be to call VTAC on 1300 364 133 and ask if irregular offer applicants are eligible for second round scholarships into their preferred course. It's toll free - the best part.

However, my
guess is unfortunately, no. I think that because as you said:
...I'm assuming that UoM would not even consider me for a 2nd round scholarship as I will obviously not have an offer for UoM on the day that 2nd round scholarships begin.
The people at UoM wouldn't see your name and as you know applying for an Irregular Offer takes time because of the number of things you need to do. I would imagine that by the time the selection officer offers you a place at UoM, all the scholarships would have been given out. Remember, this year, there's no such thing as Round 3 any more. Just round 1, round 2 and a supplementary round.
EDIT: Post edited for clarity.