This isn't a specific issue with OJS, but rather a general one with OAI. From what I can gather, the OAI-PMH protocol is designed to work over HTTP, and not SSL. See, for example, this rather old email thread on the OAI implementation mailing list:http://www.openarchives.org/pipermail/o ... 01416.html
I think that this is the case because, quite often, harvesters don't always have the ability to request documents via SSL. This is often due to self-signed certificates or certificates that were signed with trust partners that may not be supported widely.