We first have to acknowledge a fundamental disagreement that we have: you see factory farming as the problem. I see factory farming as a symptom of a more basic, fundamental problem: the belief that the other animals are commodities for humans to exploit and inflict violence upon when we have no need to. To effectively combat factory farming we have to challenge the idea that it's acceptable to inflict needless violence on the other animals.
The result we (vegans) want is an end to human violence against, and exploitation of, the other animals. The best way to achieve this is by disengaging, as far as practicable, from violent and animal-exploiting practices and encouraging and assisting others to do the same. That's the first step. Once there is a critical mass of people who embrace the vegan ethic, this will open up meaningful possibilities for collective political action.
Whatever compromises are necessary to effectively oppose human violence against the other animals.
I'd enter into an alliance with animal eaters if they are opposing things like the badger cull, fox hunting, vivisection, wild animal circuses or are trying to get cruel practices banned, such as farrowing crates or mutilations without anaesthesia. That being said, in my experience 99% of the people involved in all of these campaigns are vegan anyway.
They are the enemy - because they inflict needless violence on animals. They are also potential allies to the extent that they decide to desist from doing so, like this
wonderful man. The sort of change that I think is possible is veganism. Millions of people are already living happy, richly fulfilling lives without supporting violence against and exploitation of the other animals. There is no reason why this shouldn't be the dominant way of living - at least in a developed, industrialised society like our own.