Quickly opened up DF in adv mode. 40.03, because that's the newest I have.
The most Urist I could get is "Urist Uristurist Uristurist Urist", which is "Dagger Daggerdagger the Dagger-Dagger of Daggers", you can switch "dagger" to "daggers" before the 'the' and before 'of', but the 'of Daggers' can only been in the plural (singular and plural are the same in Dwarven). I don't know of any rules preventing this from happening in normal play, but I guess that still needs a test. Come to think, I've never seen the same word repeated twice in a name, so it's worth a check.
Test 2:
Deleted all but dark, dank and dagger from the language file (left some variation just in case it doesn't like only one word for whatever reason).
Found like 10-15 "Urist Uristurist" names in legends as the first dwarves, seems like only goblins use "dark" and "dank", that's strange...
However, goblins do NOT use "Daggerdagger" only "Darkdagger" "Dankdagger" "Daggerdark" and "Daggerdank", with filter I did not find "Ulspaulspa", which would be "Daggerdagger". It seems that the game does NOT allow repetition if it is in any way avoidable.
That's the verdict: Urist UristSOMETHING or Urist SOMETHINGurist are possible in normal play, but Urist Uristurist seems to only appear when the Dwarves are robbed of their entire vocabulary (except for Dark and dank, which they just won't use for names, probably a belief-thing)