In my experience, agnosticism is used as a qualifier with theist or atheist. See here for a breakdown of the terms. It generally follows the strong/weak labels. I am an agnostic atheist. That is, I do not believe a god or gods exists. But I don’t claim to have knowledge that no god or gods exist.
I still occasionally will find someone who is uncomfortable with the atheist label, and identifies as an agnostic. But this really doesn’t provide me with enough information. It simply ignores the question of belief altogether and skips to the realm of knowledge.
As for “strong agnosticism” – I have a difficult time parsing out the belief part of this assertion. When he/she is asked, “Do you believe in a god or gods? YES or NO”, what do they circle? There should be no problem circling one of these – even if they hold that “we can never know”. Because having a belief in a god or gods is property that you either have or do not have.
If I am asked, “Do you believe that there is a planet 20 billion light years from earth that is inhabited by creatures all named Tom?”, I will ask myself if I hold this belief or not. I do not. I do not accept the claim. Why? There is simply insufficient (no) evidence for such a claim. I do not hold the belief (atheist), yet I do not claim to know that this planet does not exist (agnostic).
Now, I could assert that there is no way for me to know if this claim is true. But I had better provide some evidence for why this is. I think when you refer to “strong agnosticism” as “dogmatic”, I think you might be simply recognizing that there is a claim being made (“I don’t know, and neither do you” or “we can never know”). And if you are going to make such claims, then you’d better come with evidence and reason to support it.
“We can never know” certainly sounds pretty strong a statement to simply accept without a decent amount of evidence and reason. But beyond that, I feel that it is insufficient to assert this as an attempt to get yourself out of the question of belief. There is an objective answer to “Do you believe in a god or gods? YES or NO”. Any attempts to merge the question of belief and knowledge seem to do a disservice to both.