It happens - shouldn't give you pause, VX has been running A320s to Hawaii for almost a year now I believe. That being said, I wouldn't be surprised though to see the A320s moved off the Hawaii routes once they start cross-fleeting since it does stretch the range of the A320 vs. the 737s.
Here's a good article from CrankyFlier about VX sending the A320s to Hawaii:
http://crankyflier.com/2015/04/09/ho...as-even-tried/