Possibly, but not as a blanket rule. The most credible reason is lower baseline dietary creatine intake, which may make the signal more noticeable in some studies than it is in already meat-eating groups.
Maybe, but the evidence is narrow. The useful question is whether creatine helps when real mental work starts to wear you down — task-switching, messages, decisions, and sustained cognitive load.
A few small studies suggest creatine may help on some tasks after sleep loss. That makes it relevant to mental endurance — not a replacement for sleep.