Disclaimer: the following is just an observation and is not authoritative by any stretch of the word.
I have Microsoft Office 365 installs in my environment, and it is detected by Inventory. In the Catalog, it rolls up under the Microsoft Office product, which is captured as the License Metric of “Install Seats”.
According to this article: Understand subscriptions and licenses in Office 365 for business Licenses are purchased on a per User metric.
Then there’s this:
How many devices can people install Office on?
If your subscription includes any of the following products, each person can install Office on up to 5 PCs or Mac, 5 tablets, and 5 phones.
Office 365 Business
Office 365 Business Premium
Office 365 ProPlus
Office 365 Enterprise E3
Office 365 Enterprise E5
Given that there is a one to many relationship possible between users and devices, tracking of your license usage in BFI will depend heavily on your business processes, and how tightly you control the installation of Office 365 components in your environment. If you can manage things so that there is only a 1:1 or 1:0 relationship between licensed users and installs, then BFI will be of help to you with reconciliation.
On the other hand, if you don’t have tight controls, or allow installations of Office 365 on unmanaged PCs, outside of BigFix visibility, or multiple managed PCS, then it will be less so. You’ll definitely need to run usage reports from the Admin portal at Microsoft, either way.