Without getting into the specifics of this particular claim (which is beyond my area of expertise) — the author of that page, Grover Furr, is a medieval historian who is also a notorious Stalinist. No real historians take any of his claims seriously; his work has all of the reliability of a bad joke. If you are interested in any topic he writes about, please look into it from more mainstream sources (which no doubt will have a range of interpretations and arguments, but Furr's stuff is totally silly). He is completely unreliable, and worse than pure nonsense. I would not call any of this work "an academic article" even though he is, of course, an academic (his PhD is in a totally different field than all of this stuff). You should regard his pages as having all of the scholarly insight and usefulness as that of the most partisan pro-Stalin blogs.

You may be interested in this answer by u/ShadowsofUtopia which outlines US and UK support of the Khmer Rouge. The simple answer is yes the US supported the Khmer Rougue for a time, mostly to cause trouble for Communist Vietnam.

Although many of the specific facts outlined by Grover Furr seem flat out wrong, the US seems to have only given them financial assistance for roughly six years and whilst Grover Furr seems to have his own particular definition of communism many other communists at the time in places like China regarded the Khmer Rouge as communist (although there is a very real argument that genocidal ultra nationalism is incompatible with being a communist).