But if you want to use DOS, try renaming and editing the inf directly to ensure the drivers are all in the 8.3 format. Personally, this is a lot of work a problem which will always be there until you move to Linux or WinPE for this.
If you do a
dir /x /s within your driver share point, you'll get an idea of just how many of your driver file names fall outside the 8.3 limitation. For me, its rather a lot.
If you are using PXE, as an interim measure you have the option of using Linux/WinPE just for the drivers filecopy. This would give you time to get over the hurdles now, and then upgrade the rest of your process to use a more modern automation.
Kind Regards,
Ian./