Can I use an extracurricular activity for a professional rec

I spend time every week working with a Non-Profit and have a really good relationship with the manager I work with there. I am planning on applying to Stanford and Harvard and both ask for two professional recommendations. For one of the recommendations I am going to use my direct supervisor at work, he will be able to give me a really good letter. I have another supervisor at work that could provide another really good letter for me, but it would cover some of the same accomplishments that the first one would. Do you think it would be better for me to get my manager at the non-profit to write a letter of recommendation for me since it would cover separate accomplishments and provide a bit of diversity to my application? Is it frowned upon to use an extracurricular activity for one of your professional recommendations?