I would guess that Sloan really thought he was acting in the best interest of the Federation - and not for personal power. He certainly had the wherewithal to leverage himself into more obvious wealth and glory, but opted to remain covert. I don't think it was because he was lazy or unambitious, considering the lengths he went to in order to win the war through his actions against the Founders. He was certainly capable of reason. Not some belligerent conqueror or power-hungry dictator.
So taking his motivation at face value here, to win the war and protect the Federation, it might be fair to call him a patriotic criminal. And while he may have maintained his cover to the death - inside his own mind, we saw how he chose to spend his remaining minutes making peace with himself through the roles of his family; I would be willing to believe they were real people. (Unless Sloan himself were a hypnotized sockpuppet for say, the brainwashing Romulans). I might have tried investigating his credentials and background after the fact, to observe how much of his cover story was in fact real. That should be easy enough to confirm for someone actually embedded within the system. Barring any possibility that he was a Q or a Romulan agent, or the like, I'd guess he threw in his hat with the Federation but played by the rules of its enemies. Which raises, actually, very real questions that people in a democracy each have to face.
Did he really love his wife? DId he really value a safe and secure Federation? His actions suggest that he did. Otherwise he might have spent his remaining moments trying to persuade Bashir and O'Brien to go rogue and undermine the Federation, not act to protect and preserve it.
Section 31 may have a longer, more deeply hidden agenda to subvert the Federation - but in the case of Sloan, this single agent did seem to believe he was acting in the interest of the Federation - and not for some deeper hypothetical consipracy. Otherwise we may have seen some evidence of doubt or regret regarding Section 31 in his last moments; or at the very least, some overarching secret revealed in his vault. No, his greatest concern at that moment was with the Founder genocide - the immediate threat to the Federation. Not some master plan for operating in various war outcomes and contingencies. As an operative, he also seemed to be high enough within the organization to be aware of any such conspiracies. So again, I'd be willing to believe he thought he was acting in the best interest of the Federation, as he averred in his recruitment speeches to Bashir.
