I posted this yesterday, but got no responses so I'm trying one last time.
I've recently found out that one of my ancestors lived in Austrian Galicia, specifically Pawlokoma, in what is now Poland. In immigration forms, his ethnicity is listed as Polish, but his religion is Greek Catholic, which from what I can tell is what Ukrainians followed.
Anyways, I was wondering what my ancestor would have identified as. Would he be considered Polish, Ukrainian, or something else entirely? And more broadly, what was national identity like in that area around 1900? Were there divisions between Poles and Ukrainians, or was it less of a clear line between different nationalities? Would all people of the same religion have been of an ethnicity, or were there Polish Greek Catholics and Ruthenian Roman Catholics?
tl;dr your ancestor was most likely Ukrainian, though we don't if he considered himself as such. I am no professional historian, but as an ethnic Pole i will try to answer your question. Sorry for grammar mistakes if i make any. Some background first. Galicia (which was the name for Austrian, later Austro-Hungarian province) had used to be a part of the Polish-Lithuanian commonwealth. The western regions (In Polish: Małopolska, literally Lesser Poland) belonged to Poland all but from the beginning of its existence, with Cracov being the capital and a great centre of culture not only for Poland. Majority of population consisted of Poles, though there were some Jews and Germans. The eastern regions (Lvov and its surroundings) originally belonged to Kievan Rus. Polish king Casimir III the Great conquered them and incorporated into Poland as Ruthenian Voivodeship (Polish administrative term, something like states in USA), though Ruthenians were given a broad autonomy (e.g. the document issued for that province were written in old Ruthenian, not in Latin). Many Ruthenians acknowleged Polish culture and language and sometimes even Catholicism, but it was mainly nobility. Peasantry remained faithful to Orthodoxy. There was also a teritorial dispute over what is usually called Cherven Cities. They were Polish lands that temporarily fell into Ruthenian hands, and thus there was a significant Orthodox (and Greco-Catholic) population. They now belong to Poland. From what you are saying, it seems plausible to say your ancestor was of that Ukrainian minority in South-Eastern Poland. There was even a known event of Pawlokoma massacre (don't know if that's just a coincidence that your ancestor came from that exact village) when Polish villagers started murdering Ukrainians. As for these immigration forms, Ukraine wasn't a state back then so he was listed as being Polish for simplification or as a mistake, if we're talking of period before 1918 when Poland regained independence.. However, we don't know if he would strongly state himself as being Ukrainian (or Ruthenian) he was probably an illiterate peasant (i don't want to offend your ancestor, in pre-war Poland illiteracy was not uncommon, though), who identified himself with his "folk", meaning Greco-Catholics from the same village who spoke the same language, rather than with "nation" as a whole. Sorry if that sound too complicated but i can't give a better response not knowing more (maybe surname?) about him. HE might have as well been a Pole who converted to Greco-Catholicism for unknown reasons, i have no idea.
Before the Partitions, when the Poland ceased to exist, it has been an almost uniquely diverse European country, so various possibilities exist.
I found some excerpts from the Austrian census of 1880 and 1890 and it seems there was no column for 'ethnicity', the only trait listed that comes close to it is 'language'. So, if your ancestor was listed as a Pole, he most likely have been simply speaking Polish as his first language (so it is likely he was an ethnic Pole in modern sense). The fact that he was Greek Catholic may complicate things, but the confession was not synonymous with ethnicity and there were many Poles following Greek Catholicism or Eastern Orthodoxy (the former was more popular in south-east, the latter was [and still is] quite common in the northeastern Poland).
As I said earlier, Poland was very diverse, and because people of various faiths and ethnicities lived together, they were mingling what led to even more complex ethno-religious mosaic over the centuries. Majority of Greek Catholics were Ruthenians (the term 'Ukrainian' emerged only in the end of 19th century) but as I said, Greek Catholic Poles were not unheard of. It is hard to say how your ancestor identified himself, but the conjecture that he at that point identified himself a Pole is pretty sound. Just don't mistake the ethnicity for political affiliation - it would be something completely normal to consider oneself a Pole in ethnic sense and Austrian in a political sense (a subject to Austrian Emperor).
On a side note, Yiddish was not listed as separate language nowhere in Austrian Empire, what indicates that all Yiddish-speaking people were automatically considered of Jewish faith (or 'Israelitic confession' as the Austrian officials called it).