I, too, would very much like the OSX Reminders to be sync'd with iCloud separately from Calendar (I, too, sync my Calendar with Google Calendars). In testing out Keen's response, I found that if I leave my OSX Calendar enabled in iCloud, then look in OSX Reminders, I see all the same tasks as on my iOS devices. On my OSX Reminders, I added a task to one of the iCloud lists. Then, once again, disabled the iCloud Calendar account. Now, when I look at my iOS device, the task I added while on my Mac is there (and alerted me on my iOS device at the appropriate time).
So, temporarily enabling the OSX Calendar/Reminders sync with iCloud is a work-around...certainly not pretty, but do-able...until Apple improves OSX to separate the Reminders iCloud sync from the Calendar iCloud sync.