one of the criteria for ulu-ness is people never heard of
it.
another one is pastors or priests never discuss it 'cos not useful
for spiritual life.
to me Amos is not ulu and I read people quoting it.
But for Nahum I'm not so sure. 
PS: With the following verses, no wonder Christians try to shun
Nahum:
1:2 The LORD is a jealous and avenging God;
the LORD takes vengeance and is filled with wrath.
The LORD takes vengeance on his foes
and maintains his wrath against his enemies.
