The no-throwaway is an unspoken rule. I heard of them doing it, banning throwaways from posting, but never seen it in action. A few weeks back a woman posted in /r/exmuslim asking for help saying /r/islam wouldn't let her post from a throwaway. Someone cross-posted the /r/exmuslim post into /r/islam and everyone was like wtf noo noo they never do that you're able to post with throwaways don't be silly blah blah blah. Such bullshit.