Maybe Roland Vincent is saying Francione wouldn't be able to get away with including dog and cat rescue in his boycott of single issue campaigns, because it is the main source of fundraising for the orgainzations, so he makes an exception for it (which is about more than just dogs and cats of course, there are lots of birds, lizards, rabbits, guinea pigs, and sometimes even farm animals seized in cruelty cases at shelters). It's a possibility that that is Francione's reason. I don't know.
As far as the OP title question, I'm not sure. Have people gone vegan as a result of the demonstrations they do? I would need to see evidence they have, and if they have, then I guess it's good for animals at least.
I went dietary vegan after listening to a Francione lecture on Youtube and the part of it that triggered me to go vegan was when he was talking about a guy in the 70s standing on a corner protesting the use of dogs in laboratory tests while wearing a leather jacket and eating hamburgers, while holding the protest sign. And he was talking about how inconsistent that is and about how "veganism is the most important form of animal rights activism".
And that idea of veganism being the most important form of animal rights activism made me take it seriously. It became something that actually counted for something to me. At the time I had been a lacto-ovo vegetarian for the prior 6 months and flexitarian for about 5 years, with long periods of dietary veganism broken up by exceptions like eating holiday meals with family that included meat, or buying my own animal products on occasion.
So I know that Francione giving that lecture made at least one person go dietary vegan. Are there any testimonies like "yeah, I was in this restaurant eating and DxE came in and did their demonstration and I was like 'well, I'm going to go vegan then'"? If there are then that's in DXE's favor.
But also worth considering, what about the other people at the restaurant who do not suddenly switch? Could the experience of witnessing the demonstration put them off considering switching to a vegan diet in the future, which they may have otherwise considered a "normal" lifestyle choice had they not encountered those "radical" DxE members at the restaurant? I don't know.
And I know that DxE does more than those demonstrations at restaurants but I'm just using them as an example because I have seen some on YouTube.