Greetings in Christ,
While I know there are no known photos of Fr. Arseny, I DO believe he lived. Yes, I am a new Orthodox Christian; no, not a Russian Orthodox Christian - but a Greek Orthodox Christian. From having met Corrie Ten Boom, not an Orthodox Christian but a Stellar Christian, I know there are Christians who have survived "camps" and be able to forgive their captors/guards. So, YES! I DO believe Fr. Arseny existed as a live person, regardless of his actual birth name, regardless of lack of photos, regardless of the lack of knowledge of his grave site. The Underground Church had, and does to this day, operate in secret and cannot do the things we in the "free" world can do. I cannot judge the actions of someone from an Underground Church - I have never lived in those circumstances.
I CAN tell you the things that a child does to survive a dictatoral and abusive father, and the actions are not so different - you do what you can to survive, even if that means doing things that are incomprehensible to those in the "normal" world - such as a lack of a show of affection, not conforming to the "norms" of the day, such as flowers on a grave, etc.