I have deployed a couple of 25G NIC based Dell Hosts in the past.  Based on my experience with hundreds of different Intel/Broadcom Hosts  i can say today its more complicated than in it was in the past.  You have to check the certified driver in combination with the right Firmware.  Speaking for Dell the FW comes always from dell.com/support and the driver always from vmware.com. But it doesnt mean that the latest FW is the one which works best or is certified.

So you need to find out the PCIID/Vendor/SubID for your given device and than go the the VMware HCL and search for the device ID (the search fields in the upper right). I always picks the IDs from the TSR which is a report i create trough the iDRAC -> Troubleshooting/SupportAssist. The TSR contains a HTML based report with detailed information.

The HCL than returns a list of all testet combinations of FW and Driver.  A async driver means that this driver is updated and provided not trough the vanilla VMware ESXi iso. It needs to manually download from vmware.com. It can be included in the $Vendor ESXi ISO which Dell and others provide.

Regards,
Joerg