You can run Hardware Asset Management in FlexNet Manager, yes.
You can set FlexNet Manager to create Device Assets from Inventory Devices automatically. This is for device created by the inventory process.
Other assets can be created manually in the UI, While best practice is to use a business adapter to import these.
Take a look at the business adapter best practice guide in the Learning Center here for some guidance on how to work with adapters.
(Anything expressed here is my own view and not necessarily that of my employer, Flexera)
FNMS does a good job of managing the assets needed to meet a SAM audit of an environment. It has a significant weakness in you must maintain either another database or spreadsheets for any asset that do not conform to the FNMS ability to run an agentless or agented scan on the device. So all your IoT items, Network gear, IP Phones, Thin clients, Blade Chassis,... will have to be maintained in a separate environment then imported regularly to keep FNMS up to date. Can FNMS be used to manage all these asset's? Yes, but it will not do it through a scan and inventory process. From a Hardware Asset Management perspective, the default behavior for FNMS is to suppress hardware purchases from the Unprocessed PO list. Pre-shipping lists of hardware would need a unique inventory adapter to stage the Assets into the table. (I haven't worked with a large number of other systems but that seems to be normal in the space)