iOS 8.1 was released today and iCloud Photo Library has been made available to the public as a beta. I'd recommend against using it for the time being.
From what I can tell, in beta form, iCloud Photo Library on iOS removes all offline synced photos (from Aperture, iPhoto, or PC) and it does not sync them to iCloud. However, it does sync Camera Roll photos across all iOS devices. Getting your Aperture/iPhoto snaps to the cloud will require Photos for OS X, which will be released next year.
Another issue to consider is iCloud storage space. By default, you get 5GB free and iCloud Photo Library will take up a considerable amount of that capacity (my iCloud Photo Library has 227 photos and 15 videos taking up 850MB). I anticipate that when Photos for OS X arrives and fills the iCloud Photo Library with my offline photos, 5GB will appear nothing more than punitive.