Apologies for the delay in getting back to you. We don't currently separate between subscription/OA types anywhere in our journal list, and that might actually be difficult to do -- the information is user-submitted, and we'd have to contact or otherwise look up the journals listed there to establish whether they are subscription-protected or not. To confuse matters further, there are of course different access types including moving wall subscriptions, so answering definitively whether a journal has OA content is perhaps a little difficult.
The best bet right now is probably to continue to rely on DOAJ -- we heavily encourage OA journals using OJS to list themselves there. But I'll bring this up with the team and see if we can provide a better solution/list from our end as well. We've been discussing whether we should set up a more "curated" version of our demo harvester (see http://harvesters.sfu.ca/demo/
), which would include only OJS/OCS/OMP content; that could be a rich source of information of the type you are looking for.