As Longstrike-haani mentioned previously, there's an old Minmatar folk legend of warrior spirits called draugr or 'again-walkers.' Though the term is mostly applied to immortal mercenaries in a negative context by only the most superstitious civilians, I've found that baring the title as a badge of pride tends to yield results within the Republic. By that I mean, people will take you far more seriously and be less likely to argue with you when you are trying to peddle a mangled flux coil to a Sanmatar.

Elysians in Gallente populations is also a common term, but you have to bare in mind that in the Federation people look to our kind more as sports stars than professional soldiers. We're a source of entertainment, and some of the more... ehm... Outgoing mercenaries like that of the infamous Kirk have a rather large following. Templars seems equally prevalent in Amarr society for obvious reasons, though the APEX line of dropsuits seems to show a shift to the alternative term 'seraphs' to mark combatants not requisitioned directly by the Amarr military.

Lastly, there is Rasetsu within the State but this term seems exclusive to shock and assault troops. More often than not troops within different specialized units will have some sort of name for themselves from Raata demonology. Baku for air assault, kappa for amphibious landings, yurei for practically anything else... Frankly, the best term I suspect that we all agree on that translates well into different cultures is a type of noble soldier we call the samurai.

Has a nice ring to it in my opinion.