I am running Resilio Sync on my MacBook Pro (Retina, 13", Ende 2013, macOS Sierra (10.12.6)). Since I have upgraded from 2.5.6 to 2.5.7 I have been experiencing around 90-100 percent CPU usage by Resilio Sync.
As far as I know, it's specifying the path for any single file download. That's a new feature introduced in 2.5.
Take a look at this article https://help.resilio.com/hc/en-us/articles/115000401010-Sharing-files-
I was able to reproduce your conflict. It indeed is greyed out now and it is not possible to enter the Photos Library.photoslibrary folder within the Resilio Sync folder selection view.
The following enterprise plans include server operating systems like the Windows Server family and all Linux x64 and x86 arch.
Sync Business with Server Support - at this moment an up to 5 users plan costs around 50€/month
Sync Business Accelerator - inc. WAN optimisation
Since macOS Sierra, your Desktop and Documents directories may get synced with iCould.
I would be careful using two different sync applications in the same directory.