Simple short question:

After activating Scapegoat, can Ultimate Offering override Scapegoats prevention of summoning?

Ultimate Offering gives you another normal summon. What you can do is to use ultimate offering to normal set, i believe.

which means no, you cannot use the ability of ultimate offering after scapegoat is activated. as scapegoat says you may not normal summon or special summon any monsters that turn. so it wouldn't matter the wording of ultimate offering either way.

You'd only be able to use Ultimate Offering to make multiple sets. You could not "override" Scapegoat's summoning restriction as Scapegoat prevents any sort of summoning in the same turn it's activated, whether it be normal or special.