There is no shortage of poor, desperate, and morally flexible (to put it mildly) Russians, period. There is no need to bring racism into it. In the particular case of Ukraine it's actually counterproductive--this "diversity" was overblown by both sides: Russians wanted to represent the whole affair as "Soviet men of all kinds defending against Ukrainian nazis", and Ukrainians wanted to see it as "an attack of an Asian horde". I understand it's hard for Ukrainians to accept that people attacking them cannot care less for their common Slavic roots, but the sooner you do the better your chances of survival.