For the most part, English-language dictionaries consider that delusional means “having false or unrealistic beliefs or opinions,” as Dictionary.com puts it.  But below the fold, a set of “Examples from the Web” includes more than one sentence mentioning “delusional ideas” — ideas that are delusions, not ideas that have delusions.  So if a psychiatrist has delusional patients, it’s a good guess that the patients are imagining things; but on the other hand, just maybe the psychiatrist is imagining patients.