Proposal: Arabic Language
Are questions about the Arabic writing system and orthography within the scope of this site? I mean questions like the placement of vowel marks, the dots under “ي” or the correct spelling of “مسئول”.
To keep it simple, the scope of this site is about the Arabic Language as a whole, which include all of it's sciences.
Of course there is علم الإملاء, which (according to google translate) is "orthography" which you are talking about in your question.
So a short answer to your questions is:
There is no need to ask if this is within the scope or not in the first place.
I would say this is definitely on topic.
Despite a lot of Arabic being written without vowels and many markings we must remember that they are there and they have a vital, complex, and wholely difficult to understand sometimes, system and set of rules.
The writing, orthography and other parts are as much a part of the language as any other part, more so with Arabic frankly, without it you do not truly understand (coming from a learners perspective here).
These questions are definitely within the scope of the site. However, as you know yourself very well, the site will be Q&A with the answer that seems to be most satisfying in the eye of the one who has asked the question being marked as the "accepted" answer, preferably on the basis of an impartial consideration of the provided answers.
Regarding questions such as the dots under the ي, it is not very likely that there could be one answer that is the most satisfying. Instead, you might get a number of answers and it would be difficult to select one as the accepted answer -- and if you end up having accepted one, it may be more on the grounds of your personal inclination than on any sort-of "objective" decision.
(Your other example about مسئول vs. مسؤول may perhaps be more likely to get a definitve answer.)
This being said, questions of this sort are nonetheless interesting and will provoke a worthwhile discussion. There is no reason, why this discussion should not be taking place on this site. I guess, all stackexchange-sites have questions that can more easily answered by a single answer and questions that don't. So we will have to figure out more generally what to do with questions that are sort-of open ended. This, however, is a methodological question all Q&A sites had to face at one point or another.
Nonetheless, these question certainly belong to the "finer points" (no pun intended) of the Arabic language. Personally, I am looking forward to questions of this sort.