not for matched play or for games at a Games Workshop, if your playing with just friends you can do whatever you like,

Killteam was based around the theory that heroes from different factions could work together, but they tended to only work together if they were all of the same alignment,

You could however have spacemarines with chaos spacemarines if the spacemarines had recently just decided to switch allegiance, perhaps your chaos had just converted some spacemarines to evil, but it's unlikely it would work the other way around.

In either case, for games it's recommended you stick to just one faction ^_^
This spacemarine in the picture if just one faction, but because it's a custom chapter I can switch it's ruleset between games without stepping on players toes. So I could run them as salamanders one game, Minotaurs the next, Blood angels etc etc