Your model doesn't need to show up in HII for you to update the WinPE image with the latest driver per that document. You just need to download the appropriate driver inf and use the WINPE Driver injection utility to import it into the WIM. You can follow this document here: How to add drivers to WinPE for Ivanti EPM OS Provisioning
Alternatively, we don't use that process because installing the drivers every single time you boot WinPE takes FAR to long and is a really silly idea. So we manually inject the appropriate WinPE Drivers. There is another document you can use here for that: How To: Use DISM to Manually Inject Drivers into the Boot.wim
As for assigning HII Drivers for that model, we run into this all the time. Our process is to just do a manual installation of what ever appropriate OS / Architecture we are using and throw an agent on it so we can scan it. The Channel and Build of Windows doesn't matter so long as its on Windows 10 or 7 or 8.1 and on the correct architecture. We use Enterprise here so we just keep a copy of the original setup ISO laying around throw it on a flash drive and boot to it. In the event Windows 10 doesn't get a network connection we'll grab the appropriate Driver CAB from Dell's website and use it to install the drivers so we can get the agent installed and an inventory run.
You can even save yourself some time by building out an MDT Share and just letting it do the heavy lifting. Here is a pretty concise article on how to do that Deploy a Windows 10 image using MDT (Windows 10) | Microsoft Docs
Ivanti Endpoint Manager is a great product... It really is... but it falls embarrassingly short when it comes to Operating System Deployment and Driver Management. In this one area I really wish they would have just copied verbatim SCCM or even MDT....