So I assume individual Armenian Orthodox faithful can venerate Severus as a Saint?
I don't see why not, and I personally don't have a problem calling him a saint.
You got to realize that 99.9% of all Armenians are completely unaware of these issues. (Same thing can be said about Chalcedon.) Among those that are aware of the issues surrounding St. Severus, you'll find different opinions.
I know a deacon with a Master of Divinity degree, who studied at Etchmiadzin. He's very scholarly, and in addition to knowing Classical Armenian, is also proficient in Syriac. In fact, he is currently translating the works of St. Isaac the Syrian from Syriac into Armenian. He has told me that the Armenian Church has nothing to do with Julianism anymore, that our Christology is identical to that of all the other OO Churches, that the anathemas against Severus of Antioch are no longer in effect, and that Armenians are perfectly free to venerate St. Severus, even though he is not on our calendar. I've heard some others express the same opinion.
Then I've known a couple of people who insist that the Armenian Church is still Julianist in its Christology, that we have a different Christology than the other OO's, that Severus is still actively under anathema, and that we should never under any circumstances call him a saint.
And then I've heard everything in between.
I have serious trouble giving credibility to the second opinion (we are still Julianist and Severus is still a condemned heretic.) This is for the following reasons:
For one thing, Julian's writings do not survive in Armenian. To put this in perspective, scholars have found the massive collection of ancient manuscripts in the Matenataran in Armenia to be a treasure trove when it comes to finding very early copies of manuscripts that have been lost elsewhere. And yet, absolutely nothing of Julian has been preserved. If his system had survived the Council of Manzikert, his writings would be found preserved in Armenian. My understanding, however, is that not only have they not been preserved in Armenian, there is no evidence that they were ever even translated into Armenian, which calls into question how widespread or entrenched Juianism ever was in the Armenian Church.
Secondly, if St. Severus were still under anathema, there would still be anathemas pronounced against him. There would, at the very least, be something dating past the early 700's. And yet it is my understanding that none have been produced since then. As I stated earlier, our priests have to read a very lengthy anathema when they get ordained. This anathema is very long and thorough, takes forever, and condemns every obscure person who ever made a mistake about God. Severus of Antioch is nowheres in there.
Thirdly, to the extent that I have met people who take the attitude that St. Severus is still a heretic, I find they can't really articulate what it is he taught that was heretical. I've asked for specifics of what it was he said or wrote that was wrong, or that differs from what the Armenian Church teaches, and I can't get an answer. Similarly, when I've asked for the difference between our Christology and that of the Syriac and Coptic Churches, I can't get a specific answer. In fact their position seems to be based on the attitude that our Church leaders of the past cannot have been wrong about something, and that if some of them once condemned Severus, then he must still be condemned and it must be for good reason. I have a problem with that attitude. While I have great respect for our leaders of the past, I don't believe any of them were infallible.
Lastly, if the Armenians still actively anathematized St. Severus, or had a different Christology from the Syriac and Coptic Churches, there would be no way that we would still be in communion with them. People are just not that tolerant.
Anyway, to answer your question above, whether an Armenian can venerate Severus of Antioch will depend on whom you ask. Like I said, I don't have a problem with it, and I get the feeling that most Armenians who know who he is won't have a problem with it.