I almost would say no, don’t do it, because if you are doing this as a work-for-hire gig, the fauxtographer will get the copyright to the photos you take for them, and may or may not let you even use them in your portfolio (depending on if there is a contract, which there should be, and what the terms are). How this person even got this gig is beyond me I guess. Your photos are better, though not amazing, but definitely better considering their awful work. If you can use the photos in your portfolio when all is said and done it may be beneficial, but if this fauxtographer is suddenly going to get lots of business based on the photos YOU shot for them, people are not going to get what they expect.
I 2nd shoot weddings here and there. I also did two on my own and one that I hired a 2nd shooter for. As for the ones I 2nd shoot, the photographer owns the copyright. They have allowed me to use the images in my portfolio after the couple received the photos, with proper copyright given and a statement that I took the photo and used it with permission. Pretty typical for a work-for-hire arrangement. It’s not a requirement for the hiring photographer to allow the 2nd shooter use of the images, but sure is a nice courtesy. That being said, I would never 2nd shoot for a fauxtographer. It would just make them look good and get them business based on my work. The photographers I have shot for have more experience with weddings than I do however I have the same skill level/similar results/similar shooting style so it all kind of blends in in the end. The one I just recently shot for hired me with a week’s notice when his usual assistant had a health issue. He was so impressed with my work and even commented that a lot of my photos were better than his. He does really nice work so that was a huge compliment to me, and from seeing some of his first dance photos compared to mine, I think mine were better. I also threw in some pose ideas he never tried that turned out amazing. Not tooting my own horn, but I think having a good working relationship with other photographers is always a good thing, but I don’t think it’ll be possible for you to ever have a working relationship with a fauxtographer. When you can each benefit from each other equally it’s a good thing.