Regarding ADOMs (Administrative Domains) in FortiAnalyzer, a fabric ADOM is capable of including all device types that FortiAnalyzer supports. This is part of the flexibility offered by ADOMs to manage and report on logs from various devices within a Fortinet security fabric. ADOMs can be enabled to support non-FortiGate devices as well, and the root ADOM in Fabric ADOMs provides visibility into all Security Fabric devices. Additionally, it should be noted that in normal mode, you cannot assign different FortiGate VDOMs to different ADOMs, while in advanced mode, you can, which provides a more granular control over the log data from individual VDOMs.
Reference: FortiAnalyzer 7.4.1 Administration Guide, "ADOMs" and "ADOM device modes" sections.