Do I need to submit an Addendum with I-485 submission for getting support from independent non-profit patient assistance programs?

May be a little touchy. You dont want to open the door unnecessarily, but you do need to proceed with extreme caution.  You may start by calling the non profit, and asking if they receive government funding.  If they do or dont, you would want some type of written affirmation, or published document of that answer. If they dont receive government funding, and you are able to get such in writing, I would still have an immigration attorney look over the written affirmation, as well as prepare your amended I- 485 if advised to still file it. If the agency is receiving government funds, it would be a decision that more likely than not, you would need to file an addendum.  In either case, because of the seriousness of the consequences, immigration legal counsel would be suggested.