Unfortunately, that doesn't really work out given that Steven Universe is an alt history: All of the states have different names and holidays like Halloween don't exist.
Gravity Falls meanwhile is explcitly in Oregon and the people of the town love Halloween so much that they celebrate it twice.
Also, Hunter's VA has said that he feels that Steven Universe would be Hunter's favorite cartoon network show citing that Hunter would very much relate to a program about love and family with a focus on healing from trauma and I don't want to give up the mental image of Hunter on the couch wrapped in a blanket watching cartoons so even if I could reconcile SU and GF I wouldn't want to bring TOH into it.*sad noises*None of our parents are cool enough to be told about the polyamory thing