If your opponent uses scapegoats, can I use Horn of Heaven to negate that summon? If so how many goats would I negate?

i do not think so. i do belive scape goats does not say summon on it. i could be wrong

gweedy is right, scapegoats aren't SUMMONED there mearly being placed after activation, thus HoH won't work on them...........

Tokens being placed are counted as special summons.

They cannot, however, be negated by Horn of Heaven because they were special summoned by the effect of another card.

Correct answer, but not the best reasoning.
Yes, the card does indees say "place" rather than "summon," but they are still considered to be special summoned.
Horn of Heaven and the Summon-Negating part of Solemn Judgement can only be used against monsters that summon themselves to the field by meeting all of the requirements. The two cards cannot be used against card effects that summon monsters to the field as they clearly state that they only negate the summoning of monsters and not effects that summon monsters to the field. The text of Royal Oppression clearly distinguishes between negating the summoning of a monster and negating the effect of a card that summons a monster to the field.

Meh...Maybe this will be clearer:

Ok I get that I think, but what about Call of the Mummy? Is it the same thing as Premature Burial or otherwise?

yes, it is.

basically either a monster like necrofear summons itself, or another card effect summons it.

so if the monster is summoned in a chian, by an effect then its untouchable by horn of heaven.