I thought the opening question was, "would you join that church?"While I agree with your interpretation, it is very possible (and was taught by many throughout the history of the church) that the Seraaphim were a type or category of angels. I don't necessarily agree, but I would not leave a church because of the Pastor believing that...it is an extremely small matter, compared to the horrific heresy that has gripped the church.
So in answer to the OP; If a pastor I was under, was CLEARLY teaching heresy contradictory to the scriptures teaching on the GOSPEL (not if he disagreed with me on what Seraphim are, or whether women should wear head coverings, or some other secondary doctrine), I would not only confront him, but I would do it as soon as the words left his mouth. If it was unclear, I would ask him for clarification after his message, and if I was convinced of his heresy, and was unable to change his mind, I would call him before the church and seek his removal. Under NO CIRCUMSTANCES would I leave the church. I would stand up during the service if I had to, to decry his heresy. I would stand outside and warn my brothers and sisters as they entered and exited if they kicked me out.
But secondary doctrine like this? No, I would debate, discuss, but ultimately agree to disagree.
I'm actually in the middle of making this decision. I was down to a choice between two churches; but then there was a split in one of them, and the pastor of the other has proven to be heavily influenced by Peter Ruckman. The second pastor has made comments similar to yours during his preaching; that we shouldn't split or depart over secondary or tertiary issues.
However, when you get to a point where you realize that after nearly every service, you're talking to your kids to explain (and possibly correct) specific points the pastor preached about, one has to ask the question: What kind of example am I setting for my children when I'm constantly telling them the pastor is wrong?
And thus, no, I would not join such a church.