Nah, the rules are pretty clear about when bonuses stack. That's why the abilities say the bonus increases. The rules about inherent bonuses only going up to +5 are limitations on the common ways to get those bonuses, not on all inherent bonuses, so I don't think it's actually breaking any rules.
You know. Something didn't quite sound right about all this… I'm very careful about planning out characters and I know I don't make mistakes because I'm just too damn anal… And I'm a rules lawyer. I knew there was a reason I picked blood Rager to make my character with both the abyssal bloodline and the orc blood line through Eldridge heritage… For the blood Rager the abyssal bloodline is a morale bonus that adds onto your rage… Then you take the orc blood line with Eldridge heritage and you get the +6 inherit bonus… So yes using Bloodrager you can make full legal use out of both the Abyssal bloodline and the orc bloodline But yes I admit the idea of taking abyssal bloodline thru VMC and then taking eldritch heritage orc would not work as they are both inherit. My mistake for listing that as a possible combo the first time I posted