I would call that a stellar record, not a mixed record. Alito makes sure the case was ruled correctly and the defendant given all reasonable appeals before allowing the killer to be put to death. Alito does not interfere in the process unless there is a problem.
I have no problem with your characterization, except I would note that it puts Alito in the Kennedy/O'Connor camp rather than the Scalia/Thomas camp, insofar as this issue is concerned.
PS. And bear in mind that this is not a case about dotting Is and crossing Ts. They are not debating whether he was correctly convicted and sentenced (that was actually rejected 9-0, at least on the basis that the legal system is inherently biased). It is a challenge to the constitutionality of lethal injection.