The oil is separating from my onion cream cheese parm dip. I added blue cheese dressing could this make it go bad?

The dressing is not bad, just too oily. Most recipes for this dip call for mayo, with emulsified fat, not dressing.
Blend with whisk or hand mixer, chill. Maybe serve as spread. Or heat gently in mw or over hot water.
Worst case, you may need to add some thickener (roux) or emulsifier.