Google wants developers to demonstrate that they take active steps against such content. The TOS of the apps you listed prohibit such content and they do remove the content if it gets reported. I doubt if Gab operates that way.
Yes but Google can always decide that because of x or x + 1 you are not in compliance and the real reason is your politics but they will never admit to it. Because Gab has more conservatives one real question is google always going to find reasons to deny when some of the same stuff is happening on twitter etc? Also does google get to decide that something say fails TOS because of support of say someone like Trump just not as famous? Does google get to decide what "such content" is? Does google get to decide who gab bans from gab's network or just which posts are censored?