Usage of the word concurrence

"Are we all in concurrence?" is not incorrect, but unnecessarily wordy. I would suggest your synonym is better, but if the word "concur" is closer to your intended meaning, I would say "Do we concur?"

An important point to note is that "concurrence" implies "all" anyway, so leave "all" off.

The words are technically synonymous, but one look at this NGram shows just how rare "concurrence" is used. In fact, the phrase "all in concurrence" reports no NGram findings whatsoever.

So, yes, you can say it's "correct", but you can probably expect to get some odd looks or even confusion if you try to use it.