The kernel is Aarch64, so you would need to use the appropriate toolchain for building. The userland is armhf, so this wouldn’t work.
sudo apt-get install aarch64-toolchain-osmc will get you that toolchain, but you’d need to build your module in a chroot.
We don’t recommend using DKMS – it leads to a lot of problems.
If you let me know the CONFIG_ option needed, I can look at getting this included for you in our kernel so you don’t need to build anything yourself.
Keep in mind that we are moving to a 4.9 kernel imminently. You should try this kernel first.