Well, based upon my own experience, I would encourage you to go ahead and contact the person, tell him/her what you are doing and see how he/she responds.
A few years ago when I was doing a sort of sub-career change within a wider career field, I had plenty of recent references who could speak to my new skills, but I also wanted someone from the past who could say that I had been a hard worker in the past. I called up a woman who had been my supervisor 15 years before. We had the nicest 5 minute phone call and she told me she was pleased to have my prospective employers contact her.
(This was the type of job application where the new employer wanted names and telephone numbers of references then the new employer would contact the ones they were interested in contacting. By contacting my old supervisor beforehand, I was able to gauge her reply. She was so friendly and enthusiastic to me about the new sub-field I was moving to that I didn't hesitate to pass alongher name. If she had sounded unsure or reserved, I would have thanked her but I wouldn't have used her name.)