I want to say:

We fought the romulans during the second and third century

So I write:

qaStaHvIS vatlh DIS poH cha'DIch wejDIch je, romuluSngan DISuv

Would joining ordinals by {je} or any other conjunction be considered to be correct?

Dunno if we have evidence, but numbers of all sorts are noun-like enough that I have no trouble treating them like nouns, even if they're not being used in the way that TKD describes using numbers as nouns.

If you want to be certain of correctness, you could of course say qaStaHvIS vatlh DIS poH cha'DIch, vatlh DIS poH wejDIch je. But I wouldn't bother.

-- 
SuStel
http://trimboli.name