In the scene with the Collector in Guardians of the Galaxy, one of the tanks in the room contains The Long One and several of the Slugs from Slither. This is clearly an Easter egg, but it begs the question, since the organisms from Slither exist in the Marvel universe, could that mean the events of Slither occurred in it as well?
I think that's more a case of James Gunn referencing his earlier work (as well as other stuff), and not canon, after all, they didn't "win" in Slither, the parasite survived, leaving the possibility of a sequel (unless Taneleer Tivan stepped in and whisked it away), so all life on Earth is left under threat.
After all, the Collectors museum contains loads of stuff, Cosmo the Space Dog, Howard the Duck, a Dark Elf, a Chitauri Soldier, the Tesseract, Adam Warlock's cocoon (maybe), Beta-Ray Bill (possibly).
Just because another film is referenced doesn't mean that all of cinematic history is now part of the same universe, so no, Nick Fury is not also Mace Windu etc, it probably follows more along the Tarantino rules.