The GPL license requires that for the entire project (the Linux kernel in this case) the source code must be available and users must have the right to make changes and redistribute the work with or without changes.
If the license on your VPN driver does not give those freedoms, then it might be technically possible to create the driver, but the combination of Linux kernel + driver cannot legally be distributed and it might be that the driver by itself is already seen as a derived work of the Linux kernel and thus let it have incompatible license terms that make legal distribution impossible.
If your company really want to use a proprietary license, make sure that your legal department knows enough about the GPLv2 and the proposed license to make an informed decision if this is a good idea. If you don't have a legal department, hire a lawyer to give you an informed legal opinion.
MODULE_LICENSE
. If you set the license to Proprietary rather than to a GPL variant, the kernel will be marked as tainted and you will only get access to a small subset of APIs. It might be better to investigate whether your proprietary functionality can be provided in userspace.