If you will be going on Disneyland Dr. to get to DTD, you'll have at least two choices (depending on the construction, which is still pending, pending, pending...):
1. Cross at Magic Way, then enter the path (right on that corner) to M&F, go through bag check there (usually very quick and in the shade), and take the tram to DTD. If it's really hot that afternoon, this might be a good option.
2. If construction on the western end of DTD has already begun (basically anything west of the monorail track will be demolished at some point), then you can walk to the parking lot just past the PPH (the lot behind the AMC building) to what will be the new bag check there (should be by the monorail track and the back of the
Lego Store). You'll be able to enter DTD from there. (Disclaimer: this bag check hasn't opened as of today, so check back before your trip to see if it is open to you by then.)
After the party, you should have no problem exiting through the GCH to Disneyland Dr. That is totally allowed. If you do this, enjoy some time in the lobby and take some photos before heading back to your hotel!
Don't be alarmed if the lines for DCA appear really long when you arrive. Sometimes the lines can look a bit scary when the early party hours start because lots of MHP guests park hop right off the bat. The lines will move, so hang in there! (And if Oogie is decorating the DCA front entrance again this year, listen up! He talks!)