1. Is Huxley's Agnosticism compatible with The-ism and Athe-ism? No.
Huxley clearly states that it isn't compatible with Athe-ism or The-ism. He also clearly states what the most important parts of Agnosticism are:
1. Agnosticism is of the essence of science, whether ancient or modern. It simply means that a man shall not say he knows or believes that which he has no scientific grounds for professing to know or believe.2. Consequently Agnosticism puts aside not only the greater part of popular theology, but also the greater part of anti-theology. On the whole, the "bosh" of heterodoxy is more offensive to me than that of orthodoxy, because heterodoxy professes to be guided by reason and science, and orthodoxy does not."Positively the principle may be expressed: In matters of the intellect, follow your reason as far as it will take you, without regard to any other consideration. And negatively: In matters of the intellect do not pretend that conclusions are certain which are not demonstrated or demonstrable""This principle may be stated in various ways, but they all amount to this: that it is wrong for a man to say that he is certain of the objective truth of any proposition unless he can produce evidence which logically justifies that certainty. This is what Agnosticism asserts; and, in my opinion, it is all that is essential to Agnosticism. That which Agnostics deny and repudiate, as immoral, is the contrary doctrine, that there are propositions which men ought to believe, without logically satisfactory evidence; and that reprobation ought to attach to the profession of disbelief in such inadequately supported propositions."
He maintained that the Agnostic position should be skeptical, and to not believe a proposition without logical satisfactory evidence. This is not compatible with being an Athe-ist or The-ist. Should one accept evidence as logical, you then become a believer, and are no longer skeptical of the proposition. It is impossible to both believe a proposition is true and doubt (be skeptical) that a proposition is true.
2. Does Huxley's Agnosticism state that anything is unknown or unknowable? No.
Huxley does state that answers are unknown to him, personally, and that he, personally, thinks they may just be unknowable. However, he also clearly states that his lack of knowledge doesn't mean that the answer is unknown to someone else, or will forever be unknowable in the future, though he may have a strong opinion on the matter.
"The extent of the region of the uncertain, the number of the problems the investigation of which ends in a verdict of not proven, will vary according to the knowledge and the intellectual habits of the individual Agnostic. I do not very much care to speak of anything as "unknowable." What I am sure about is that there are many topics about which I know nothing; and which, so far as I can see, are out of reach of my faculties. But whether these things are knowable by any one else is exactly one of those matters which is beyond my knowledge, though I may have a tolerably strong opinion as to the probabilities of the case."