I've been playing conquest lately and... I strangely love it. The rules were written by a 8 year old in Norway so it's almost impossible to understand some of the more complicated rules but FF is doing a good job with the Warhammer 40k IP with this game.
For the sake of fluff, even though it's scant:
With Sicarius and Shadowsun present I would say that this even took place during, or is a part of, the Zeist campaign with the Tau planet Y'varn and several Imperial/other faction planets. I would make the assumption that this is toward the galactic core and beyond the damocles gulf. Perhaps it takes place during the advance of the 3rd Sphere around the same time as the 13th Black Crusade.
The planet Y'varn is in the Traxis sector (a region in the Ultima Segmentum that is being discovered by the Imperials and invaded by the forces of Chaos simultaneously).
The planets of the Traxis sector are as follows:
Tau VIP's in the area are: Aun'shi, Shadowsun and a Commander Starblaze who uses Guard units:
From FF: Strange Alliance
The Tau Empire has expanded quickly into the Traxis sector, and their guiding principle—For the Greater Good—has proven attractive to many, even those who once fought for the Emperor of Mankind. Some Tau commanders are known for accepting humans into the ranks of their armies and giving them the chance to prove their new devotion to the Greater Good. Commander Starblaze is one such leader.