Combat Pragmatist: Despite their reputation for honor, the eldrae in general and the Imperial Legions in particular are very much the combat pragmatists. (An immortal life, after all, is a very precious thing, both individually and demographically.) So while they would much prefer to resolve conflicts through other means, including delightfully fair and stylized “game war”, if it actually comes down to it – well, let’s just say that no-one ever told them that war ought to be sporting, and that idea would be good for a laugh at the Admiralty any day of the week.
The general view of said Admiralty is that in a real war, if you’re not cheating, you’re fixin’ to lose. Special operations (including assassination) are pretty much the best ways to make war, with sneakiness, ambush, infiltration, deceptiveness, preemption – and only a complete idiot or a lunatic would announce to the enemy that they’re about to attack them in advance – and avoiding a fair fight at all costs making up most of the rest of the doctrine. While in regular warfare, they take pains to preserve civilian lives and local property values, that’s because it’s also moderately stupid to destroy the asset value of whatever you’re fighting over – if you care to keep military assets around your civilians, provoke them to a no-rules war, or engage in asymmetric warfare, you can find out for yourself that this is not an absolute rule, it’s merely a moral preference – and in the latter case learn that Disproportionate Retribution is also the order of the day (on the grounds that the ideal response is one which precludes any possible necessity of its repetition).
Much the same principles apply to individual-level combat; most of the Empire’s prized schools of armed and unarmed martial arts explicitly include a wide number of moves which humans would call, ah, “ungentlemanly”, including the virtues of the Groin Attack, shooting people in the back, and other extracts from their millennia-long collection of dirty tricks. Of course, what they’ll tell you is that if a gentleman is required to fight, he’s fighting for something, and that that something is not going to be served by voluntarily conceding the advantage. He is, therefore, obliged to use all the means he has available to win it.
(That the contrast between their general “honorable” behavior and combat pragmatism causes cognitive dissonance in a remarkably large number of species and cultures is, incidentally, something else that they shamelessly use to their advantage.)