Upload it where?
Creative Cloud isn't really an online storage solution, you know. Yes, you get up to 20gb of online space as part of your CC deal (depending on which deal you choose), but it's not (say) a Crashplan alternative.
Yet when you go to the Creative Cloud page (https://creative.adobe.com/files), it clearly says:
"Store your files in the cloud to access your creativity from any device."
(an Icon with the words) "Photos Go Here"
So, Keith, what exactly is the CS Cloud to be used for?
The Cloud is for licensing and distribution of Cloud products although there is a cloud storage component.
That statement about storing your files in the cloud for access from any device is about individual projects you’re currently in the middle of, not all the photos you’ve ever taken or the LR catalog that is pointing to all of them.
Think about if you’re a graphic artist working on an advertisement for Vogue magazine and you need a few images a few fonts and a few documents saved out of Photoshop or Illustrator or other cloud apps, those files for your work-in-progress, can be stored on the cloud and then synced down to your local computer while you’re working on them, and then sync them back up to the cloud when you’re done with an editing session, so they’re available for wherever you have time to work on them on another computer somewhere else.
That is just an example. You can use that storage for whatever you want, but the size and most bandwidth limitations aren’t going to work for a huge file that is meant to be stored on fast locally-attached storage. The cloud storage is not a remote disk-drive.
The answer to the original question is both "It depends..." and "it's always changing."
In the beginning, Creative Cloud storage was just about sharing a few project files. More recently, they finally added the ability to share folders. Since Lightroom Mobile came out, you can now use Creative Cloud to upload photos from your Lightroom catalog. But not exactly in the way that you asked. You can't just upload all your raw files. You select specific Collections in Lightroom, and Lightroom will make Smart Preview copies of them for efficient transmission and lower storage usage on mobile devices, and upload those Smart Previews to your Creative Cloud storage. You can then edit them using Lightroom on mobile devices, or you can also get to them (read-only) through your web browser when you click the Photos link on the Creative Cloud website. If you edit the mobile versions, the edits sync back to the originals in Lightroom on your desktop.
If you use your Creative Cloud storage for Lightroom Mobile syncing it does not count against the 20GB storage limit, though Adobe doesn't say what the limit for LR Mobile actually is. They assume it's self-limiting because most people don't have 20GB free on their mobile devices anyway.
So that's the "it depends" part. You can upload your Lightroom images to Creative Cloud storage using Lightroom Mobile, but not in their original format, and probably not 400GB of them. Also, right now you can't use LR Mobile to edit your LIghtroom catalog from another computer.
The "it's always changing" part is that over time they have been adding new ways to use that storage. If the way it works now isn't what you were looking for, wait a while and check back.