Not to be difficult, but I do not see a dilemma here. I am thirty years vegan now and work with mostly non-vegan clients. I do not push them to be vegan, just as I would not push someone to my political views or my religious views. I direct them within my scope of practice regardless of their lifestyle or ideology.
I do refer most of my clients to a registered dietician when they want/need specific guidance in proper nutrition. I do explain nutrition within my scope to those that want me to do so. When it comes to protein, we discuss their potential options. This includes all potential sources of protein. I do work with several vegan clients. For the most part they are on it nutritional speaking, but I have given them guidelines as well when requested with the protein focus on vegan sources.
If you would like to discuss this further, contact me through my profile or my website, www.hawaiifitnessacademy.com.