I would say if it was known that the person hadn't been baptized, and thus a baptism of blood (so similiar to baptism of desire), then the answer would likely be yes.
I do wonder though how one would account for someone baptized, in mortal sin and not having made a perfect act of contrition and not getting to confession before dying as a martyr. It would seem possible, given Church teachings, that a person could die for the faith and not attain salvation in that situation.
Thus, we can't say for certain that the martyr would be heaven bound because of circumstances we don't know about. And a possibility their death wasn't purely their choice to die for the faith and other factors.
Marcia