If the XCMD comes with a sample stack, that stack will be uploaded. If it's just an XCMD it may be trickier. If you find any stack that isn't working because of a missing XCMD (or any other reason) then let me know - hypercardonline@gmail.com

Given that there's a topic "hypercard_xcmd-xfcn" I'd wager they are. Archive.org is essentially emulating a Mac Plus that runs HyperCard in the browser.