There are different types of bipolar disorder: Bipolar I is the traditional, most widely recongized form of bipolar disorder, usually involving recurrent episodes of mania and depression (about 10% of people with this diagnosis never suffer major depression). In order to receive a diagnosis of Bipolar I, you must have experienced one or more full-blown manic episodes that cannot be attributed to other medical conditions or the use of drugs or alcohol. It's not uncommon for people with Bipolar I to experience psychotic symptoms.
Bipolar II involves periods of major depression and at least one episode of hypomania - this is what I refer to as a "mini-high", rather than a full-blown manic episode. People with this form of bipolar disorder do not experience psychotic symptoms while in a high state. However, psychosis can occur during depressive episodes as well, whether unipolar or bipolar.
So the bottom line is that, while bipolar II can cause psychotic symptoms such as hallucinations, this doesn't happen while in a hypomanic episode (if psychosis is occurring during a "high", this is by definition no longer a hypomania, but a mania), and is therefore much less common than in individuals with bipolar I.
It's also important to point out that not everyone with bipolar I experiences psychosis.