It certainly is. Both manic and depressive states can have psychotic features, and because mixed episodes are some sort of combination of both states, hallucinations, delusions, etc. can definitely be present. From what I've been told and for what I can remember, I've only experienced delusions and/or their little sisters 'ideas of reference' while in mixed states, but for whatever reason never in predominantly manic or depressive states.
Yeah, I hallucinate and I only do it during mixed episodes. I'm bipolar.
As a person with schizoaffective before my current recovery I did. That can also occur in people with bipolar with psychotic features. Discuss this with your psychiatrist and ask if psychosis is part of your diagnosis.