The UNSC is under attack by The Dominion. In order to make this a fair fight, the UNSCs weapons are upgraded to Star Trek weapon standards on both ship and infantry.
With these weapons, the UNSC is ordered to hold AR-558. Federation troops have been withdrawn. AR-558 is being defended by 2 battalions of Marines, 1 battalion of ODSTs and 10 SPARTAN-II. The SPARTANS are led by Master Chief.
Is AR-558 held?
__________________ "Great men are forged in fire. It is the privilege of lesser men to light the flame . . . whatever the cost"
To be more up front though with threads like this, I think the term is "force sub." You're not actually pitting the UNSC against the Dominion, you're subbing them for the Federation troops on AR-558.
As to the question: maybe. I want to say yes, but I don't know how many Federation troops were holding AR-558. If it was just the ones we saw, then there's no question that a much larger UNSC force led by Master Chief would do the same job, but if we're talking about tens of thousands of Federation troops scattered around the planet (which would make more sense) then I don't think the UNSC has the manpower here to cover the entire planet.
“Where the longleaf pines are whispering
to him who loved them so.
Where the faint murmurs now dwindling
echo o’er tide and shore."
-A Grave Epitaph in Santa Rosa County, Florida; I wish I could remember the man's name.