i worked on pytype for several years, and occasionally had to support projects that wanted to use multiple type checkers. in my experience, there were definitely times when one type checker would pass some code and another one reject it, but not code that would strictly work on either one checker or another but not both. it could be a pain trying to keep the strictest type checker happy when the other ones passed your code, but usually once you did that you were fine.
also if you do find a case where two type checkers genuinely conflict on a piece of code, one or both of them would definitely like to see it as a bug report. if the underlying cause turns out to be undefined behaviour in the specs, the general typing community will work together to nail it down and the type checkers will all adapt. in general it is a very cooperative process that values the existence of a common set of standards, which is why I think having more type checkers will only improve the situation wrt nailing down corner cases in the specs.
also if you do find a case where two type checkers genuinely conflict on a piece of code, one or both of them would definitely like to see it as a bug report. if the underlying cause turns out to be undefined behaviour in the specs, the general typing community will work together to nail it down and the type checkers will all adapt. in general it is a very cooperative process that values the existence of a common set of standards, which is why I think having more type checkers will only improve the situation wrt nailing down corner cases in the specs.