Thanks for the correction, Ascenray. Of course you’re right, I did indeed have it backwards–it’s the ‘official Youtube administrator’ for countless publishers, but that doesn’t mean it’s on YT’s payroll. So, I appreciate the nitpick!
BTW, as an aside, some time I would really like to pick your brain as far as copyright issues go, because you (along with Exapno Mapcase) are reliably on target whenever the topic pops up, and it’s always informative to read your comments.
That explains it. 
Almost certainly not. They are most likely just like yours truly. Youtube sent a note giving me the option to include ads or delete the video, and I said, “sure, ad me up, baby; it’s the least I can do if it’s someone else’s copyright.” (I paraphrase.)
I’m sure a notable (even if only a minority) percentage of the more professional or semi-pro bands who do actual covers are indeed contacting HFA or the other copyright holders directly. But I’m also quite sure most of us just accept the ads as a necessity if we want to use someone else’s material. It’s basically a free way for us to pay the royalties we owe. I’m perfectly fine with it, myself.
aceplace57, yes, I’d stay away from any of the "popular’ Christmas songs from the 20th century (stuff like “White Christmas,” “Rudolph the Red-Nosed Reindeer,” “Have Yourself a Merry Little Christmas,” and so on) as opposed to the traditional ones like “Adeste Fideles” or “Silent Night.” Even with them, if you’re not planning on using your own arrangement, I’d double-check to make sure the arrangement itself isn’t under copyright. But in general if you want to record yourself singing “Here We Come A-Wassailing,” “Hark the Herald Angels Sing” or “The Holly and the Ivy,” you’ll be fine.
Two interesting exceptions: “Twelve Days of Christmas.” It’s a traditional carol and thus everything’s public domain…* except* the “Five Gold Rings” line, believe it or not. That two-measure phrase is a relatively modern touch that’s copyrighted. The words aren’t original but the little tune that goes with 'em* is. So as long as you don’t use that particular tune --substitute any other notes you wish–you’re, um, golden. 
The other is “O Little Town of Bethlehem.” This I could be wrong about, but… I believe the copyright nature here depends on which melody you use: the standard American version (which is perfectly kosher to use), or the British one, which uses a traditional tune that’s been rather liberally adapted by Ralph Vaughan Williams. His version’s actually still under copyright, at least in the UK.
But honestly, while publishing it would be marginally more worrisome than just singing it, even then there’s little likelihood that you’d get a Cease and Desist from the owner. It’s been used generically for so long and they don’t appear to pursue violations. HOWEVER, since you’re asking about legit/correct practices, proper behavior would be to contact the owner. OTOH, you can just improvise off the original “Forest Green” tunewith your own arrangement and none’ll dare come after ye, since “Forest Green” is public domain. (That sheet music isn’t, of course.)
- You know the one. Assuming we’re in C major, the melody is: “G (held for a half-note), A (eighth), F# (dotted quarter), G (whole)…”