In general, I think you can always post a question on the main site (assuming it is on-topic, which your example is). It is always better to do a bit of research to see if it has been asked before, but even if you don't or can't it is not the end of the world. If someone later finds that the question has already been asked, they can simply then close yours as a duplicate.
In this particular case, I did a quick search and did not find such a question yet on the site. While it's certainly possible that I missed it, and it has in fact been asked (and I did not do anywhere near an exhaustive search), I don't think there should be any problem with you asking it.
Of course, if you do ask it it is always best to include as much detail as possible – including why you think there might be such a tradition.
If you want to look at relevant tags, we have a tag for the Binding of Isaac, as well as a tag for Passover.