Yes, most projects implement validation of some sort as even well-intentioned BOINC users will occasionally submit invalid workunits due to computation errors, random memory bits flipping, etc. Validation schemes range from simple to complex but suffice to say yes they nearly universally have some sort of validation mechanism. People have attempted to cheat BOINC before simply in pursuit of a “high score” compared to other users, so the BOINC ecosystem is well acquainted with proper defenses for such behavior. There are even cross-project competitions people can participate in, people join teams etc, so the competition can be quite fierce.