Windows Setup media boots to WinPE. WinPE reports itself as a client operating system when loading drivers.
Any driver used to access an iSCSI disk for deployment must allow installation on both client and server operating systems SKUs. Additionally, the driver must be signed in 64-bit scenarios.
If the device is supported for Server operating systems only or the INF for a 3rd party driver explicitly blocks installation on client SKUs of Windows, you will not be able to load the required 3rd party driver in WinPE, and therefore you will not be able to deploy to an iSCSI disk.
Contact your driver vendor if you have a 3rd party driver which blocks installation on client operating systems SKUs.
iSCSI boot deployment Setup driver WinPE