As far as I know, in the Yemenite tradition there is a distinct sound for all consonants for the exception of Samakh and Sin. In the Wikipedia, it says that both sin and samakh are pronounced identically as /s/. However, I have found two responses here of that at least in in some sub-dialects of Yemenite Hebrew, there was exists or at least at some point existed a distinction between the two letters.
Examples of this are here and here. I've searched around the web looking to see if there was any other source that would indicate the existence of between the voiceless sibilants. After much searching, the only lead I could find of people talking about a difference was on the old teimani website chayas here as a comment from the site admin. I can't trust the source for sure but if such a distinction did exist in recent times, could any of you present me a good source that talks about the difference between samakh and sin according to the Yemenites, if it exists?