"While Sony retains the film rights and receives all revenue from the movie itself, Marvel - in exchange for making the movie - can use Spider-Man in their own Marvel Studios films, and also reap any rewards from non-movie uses of the character such as in merchandise and video games, which Marvel retained the rights to."
I could see a character making a cameo in the Homecoming sequels because Marvel is still producing those. But Feige has come out and said that the Venom movie is not part of the MCU so i doubt anything else would cross over besides Spider-Man himself and in the Homecoming sequels
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in the middle of filming. Wtf....
https://www.newsarama.com/35027-kraven-mysterio-carnage-another-mcu-hero-part-of-sony-s-spider-man-franchise-plans.html
It also says absolutely nothing about MCU characters appearing in Spider-Man movies, let alone spinoff films like Venom