I've never seen it documented but I believe that Illustrator graphics are saved it the CC libraries as PDF files. Other applications cannot work with AI files directly.
You could place the Illustrator file into InDesign to view how this artwork works if you place an AI (in which case it will display the PDF).
When you're placing an AI file or an AI graphic from the CC libraries, you will not be able to edit it in InDesign. If you right-click on the graphic in the Library, choose Place Linked. If you need to edit the graphic, right-click graphic in CC Libraries and choose Edit. This will open the graphic in Illustrator (as a temporary file). Save the edits and it will be updated in the CC library. Then the graphic will be updated in InDesign.
I think Steve and Use already answered question 2 for sure. Regarding those logos that don't appear… One thing that confuses users, is that if you add a placed Illustrator file to a Library from within InDesign, it's adding a reference to the placed graphic on your hard drive or server. So when you re-use that asset, you still need access to the location of that original asset. For better and more reliable behavior, open the logo in Illustrator, select the artwork, and drag it into the library. This is now a native Illustrator object that "lives" in the cloud entirely. So when you place this in InDesign, it's actually referencing the artwork in the cloud. I'm not positive this is what you're encountering but it appears that way. Hope that helps!
I totally agree with Chad: When you're adding the Illustrator graphic within InDesign, you can't edit it. If you add the Illustrator graphic within Illustrator, it becomes an editable object.
Thanks so much for your replies, is not working for me though. If I copy this logo in Illustrator 2018 and paste into InDesign 2018, I cannot edit that paths and recolor fills, like I used to. Also Indesign trims the logo so the bonding box does tho include the shapes filled with nine, I use as a graphics safety zone around logo.
I recreated the library item from CC2018, so that seems to have resolved the issue of the logo coming up blank. Seems the version you use to add to the library makes a big difference, as I encountered this in using just Illustrator alone.
The URL will expire on Dec 13.
Also the layer names from Illustrator are not remembered anymore. This seems to be a 2018 issue as the layer names used to hold in Illustrator 2015 & 2017 which was very useful. Now library items drop onto the layer you have selected. To me in a design environment that goes to final print is not good, as this promotes items going onto the wrong layers and you have to switch layers more often.
Copy and paste from Illustrator only works with extremely simple objects:
Only if it's within that limit is it editable. If it's more than that it's embedded EPS or PDF file which can't be edited.