While StubHub may be a legit company, they are still selling Disney tickets that state they are "not for resale." The OP should call the on site hotels again, just to check with another CM. Other people on these boards have been told that there
will be same day tickets available to on site guests only first thing on the morning of each party. No one has reported back yet this year that they did purchase same day tickets this way. Some people reported last year that they were able to purchase 1 extra ticket by going to the ticket booths with someone who already had tickets. If the person could show the CM that s/he already had MHP tickets, but needed one more, they could purchase one more. This had to be done first thing when the booths opened.
To the OP:
MNSSHP is at WDW; MHP is at DL. Just a clarification in case people looking at the title of your post think you want tickets to WDW. Also, there have been reports in the last few years of people buying MNSSHP tickets on unauthorized sites, then trying to use them very unsuccessfully at DL. Good luck getting your tickets!