The Space Marines were made to destroy Xenos, so using that logic they're out of any alliance already.
Funny ive been talking about this for a loooooong time . . . So yeah I suppoz wez could work sumtin out. We orks was gonna krump dem panzies an spacy mareens anyway so dis fits right in wit our plans. So yeah just hand over all your flash an shooty dakka an yur trucks an yur tanks an yur shiny bits and we'll get right on it. Wot? use it against ya? Naw nevar. What makes ya tink dat? We didn't eat your cultists im like 50% sure. And that bloodthirster always belonged to us yeah, see its painted blue....
nej det var jag! and anoverthing wats wiff all dis talk of da brain boyz i thought wez was takin aboot wever or not we fight together or agitnst eachover