You indicate that the packages upgraded correctly, and you can use it right now. So if it works, you can use it like that. However, I suspect it is not officially supported.
I take it that your hosting provider uses OpenVZ (or it's commercial equivalent, Odin Virtuozzo), or some other Operating System-level virtualization (as opposed to paravirtualization, like Xen of KVM provides).
For me it, worked in practice, and since I don't see any problem, I'll use it with the older kernel. I followed the guide at http://justinfranks.com/linux-administration/upgrade-openvz-vps-from-debian-7-wheezy-64-bit-to-debian-8-jessie-64-bit (albeit my VPS is 32-bit instead of 64-bit).
That said, I suspect this is not officially supported by either Debian or Odin Virtuozzo/OpenVZ.
If you want official support, you should wait till your hosting provider offers Debian 8 support, but I suspect that you will have to reinstall your VPS in that case. They are probably waiting for the support of Debian 8 from OpenVZ or Virtuozzo. It seems that support is coming soon: See https://wiki.openvz.org/Download/template/precreated and http://kb.odin.com/en/125613.