ZFS and kernel 5.0

Currently on Ubuntu 18.04 and I like to upgrade with the latest kernel, is it compatible to run LXC with ZFS support on Linux kernel 5.0.x or ideally to stick with 4.x?

Is zfs-dkms require to rebuild ZFS module to use with LXC?

The stock Ubuntu Linux kernels have ZFS compiled as modules (no need for DKMS and any additional steps from your side), and you are fine to use any stock Ubuntu Linux kernel.
If you really need to run Linux 5.0 now, you can upgrade or install Ubuntu 19.04 that was released yesterday. It also has the proper ZFS support.

If you install some other kernel, you need to provide ZFS yourself. This includes the kernel from the PPA.

Having said that, if you stick to 18.04 now, then you can get the proper stock Ubuntu Linux 5.0 kernel around August, in the 18.03.3 update.