Is Hetalia a Yaoi anime/manga?

No, it's not.
It's just a parody of historical events and politics between countries. As the matter of fact, Hetalia's main demographic/targetted audience isn't even girls.
The original manga is a Seinen manga while Hetalia World Stars is Shounen, both targetted towards male readers.

I've noticed that most of the people who are claiming it's shounen-ai/yaoi are either people who haven't watched or read Hetalia and simply assumed its genres or they're the same teenage yaoi fangirls who are also claiming that Haikyuu and Kuroko no Basket are shounen-ai. Not really that reliable, in my opinion.

Then there are the fans who think Hetalia /should/ be categorized as shounen-ai. However, thinking that a certain anime and/or manga should be considered as shounen-ai doesn't make it shounen-ai. At the end of the day, Hetalia is still just historical satire.

No lol.