Homework?
Unstated facts can influence my answer - No.
Goes to relevance. Prima facie the defendant having a violent nature is not relevant. What unstated fact is likely to make the opinion evidence relevant to a fact in issue? Tendency or coincidence MAY bring the opinion evidence in but the evidence from the expert would need to be very compelling and unique in some way, and even then the judge's discretion in s135 or s137 may keep it out.
And is there any kind of privilege that might apply between the defendant and the expert? For instance, how did the expert form his opinion about the defendant?