FYI - there are many non-smoke methods of using medical cannabis - including vaporizing (so no smoke), edibles from tinctures, lozenges, cookies, butters, etc.
There are many medical conditions that medical cannabis can be helpful for - arthritis, pain, MS, nausea, etc. I'd like to do further research about cannabis and OSA.
If one is serious about using cannabis for a medical reason there are many methods other then smoking that can get it into your bloodstream and for longer duration then just an hour or two. I do not currently use medical cannabis but have looked into it. Smoking is not the recommended way to use medical cannabis do to the effects of burnt plant matter.
Due in large part to Governmental regulations and the bias of both the medical community and its funding, the studies that can be found are often very conflicting. There are though many good cases for medical use of cannabis. Cancer patients, people with seizures report it aids in controlling them, I even saw a guy on one documentary that took a high velocity sniper round to his skull and survived with over 45% of his grey matter being effected, he once took many meds to control some of the issues that developed but found cannabis more useful for controlling them. Some of the issues included sezures, sensitivity to hot and cold, difficulties in eating, not to mention the depression. When they guys brain started healing and rerouting functions one of the most fun things he talked about was how for the one whole side of his body now registers cold as pain. An ice cube run across his arm feels like a razor blade being drawn over his arm. I figure after the guy survived a sniper shot to the skull if he wants to use hash and it helps him deal with his issues LET HIM. The use helps him be happier, dulls his sensitivity to hot and cold, and as he now has metal holding his skull together and seizures are bad, helps stop them without the heavy side effects of other medications for seizures.
This all aside I do feel that cannabis does have a medical value but it needs proper research and the restrictions for said research to be relaxed.
For a replacement treatment of OSA though? not bloody likely, at best I could see it as an aid to be comfortable with the mask, aid with anxiety for some with the goal mainly to get to sleep.