You've raised an issue that has fascinated me as an amateur Hagiographer! ("Amateur" only in that I love doing it, and not that I'm not really good at it
Fr. Elias raises the issue of whether Catholics who are killed by other Catholics can be martyrs.
In fact, the Catholic Church has formally declined to say so.
This comes up most forcefully in the discussions surrounding the Cause of Jerome Savonarola who was the Apocalyptic Florentine Monk burned at the stake, along with two other Dominican confreres, for prophesying against the sinfulness of the city's inhabitants, including the Borgias etc.
The Dominicans have always venerated Savonarola privately and in Florence and elsewhere there was even a cult to him with Masses of devotion to him, medals struck of "Blessed Jerome Savonarola" and the like.
St Philip Neri and St Catherine of Genoa both revered Savonarola and Neri even wore a medal-relic of the fiery Dominican reformer on his chest.
The "Devil's Advocate" in Neri's Cause even proposed that his veneration for Savonarola, who had been excommunicated by Alexander VI, should be stopped for this reason. But the matter was ordered "passed over."
Pope Julius II had a picture of Savonarola painted in the Vatican, but without having Jerome's name printed on it so few would know who this really was. Julius II wanted to canonize Savonarola but was persuaded otherwise since the Borgias were around and might be offended.
The pope was also asked how a martyr could be declared when it was the Church itself that condemned him!
The pope said, "The confession of sin is not what pollutes, the sin itself is what pollutes."
There is a society that advances the Cause of Savonarola (indeed, Met. Andrew Sheptytsky was a member of it and before his death in 1944 a book on Savonarola's life was found on his bed).
But some Catholic scholars still argue the question as to how someone could be declared a martyr if it is the Church itself that martyred him or her?
One way around that, as happened in Joan of Arc's case, is to simply defer declaring a Saint a "Martyr" and just be content with the sainthood status.
Fr. Holweck (are you making footnotes, Gerard?
in his "Dictionary of the Saints" that was last published, I believe, in 1924 at least my copy was, does list a number of interesting cases in this regard.
He lists the Orthodox St Isidore and the 72 Orthodox Martyrs at Dorpats in Estonia as "Martyrs for their Rite and nationality" as they were killed on orders of the RC Archbishop for refusing to become Latin Catholic (not even "uniates!").
When Orthodox groups come into union with Rome, the practice is that overtly "anti-Catholic" Orthodox saints are dropped from the calendar. The Ethiopian Catholics had "St Pontius Pilate" dropped from theirs.
But normally we don't question each other's canonizations. And, of course, one Church is not required to receive the cult of another's local, regional or even national saints.
I doubt very much if St Peter the Aleut would ever be accepted in the Latin Church, precisely because he was martyred at the hands of Catholics.
But who knows?
The point is how we interpret the life of Peter the Aleutian.
If we say he is an Orthodox martyr at the hands of the Latin heretics etc. that may pose a problem for Eastern Catholics
If we see him as a Martyr for the Christian traditions he recieved as an Orthodox and who refused to be baptized again having been baptized already as Orthodox, then there should be no problem.
I think we have a better grasp of historical context today. Even St Mark of Ephesus whom Holweck calls that "Furious Schismatic" when seen in his proper historical context and with more information available to us is not that at all.
He was, in fact, a pro-union Orthodox prelate who put down the removal of the Filioque in the Creed as the minimum and really only requirement for the restoration of unity. But then we know the rest of the story.
There are also two Akathists to St Vladimir the Great, one Orthodox and one Catholic. They differ by one line where the Orthodox state that he rejected the Latin heresy for Orthodoxy and where the Catholics say he preferred the beauty of the Orthodox liturgy over all others.
It really is all a matter of interpretation.
St Alexis Toth whom many Eastern Catholics honour often referred to Basilian priests as "jerks" in his diaries.
So where does one draw the line?