Bjørn, you're worried about something that isn't an issue. In your case, you have a hypervisor and four virtual machines. One of those virtual machines (the management OS) came with the hypervisor. You then installed three virtual machines.
Ask yourself whether you'd like to see the management OS using CPU time. Ideally, you want it to leave as much CPU time as it possibly can to the three VMs that you set up.
This is exactly what Hyper-V does, assuming that you have installed the "VM Integration Components" in all your VMs. These components make I/O much more efficient by installing drivers that are meant for VMs. Then, unless your VMs are particularly I/O-heavy, your management OS will just sit there waiting for you to interact with it, attempting to use as few resources as possible. This is a good thing.
If you want to see the actual CPU metrics from the hypervisor, not the management OS, use Performance Monitor in the management OS and look for the Hyper-V counters. These will tell you about physical CPU usage.
Doug Luxem (who seems to know a lot about this) answered this well on another thread today. So I'll just steal his text:
First, you have to remember that in
Hyper-V that the "host" is called a
parent partition and it really just
like a virtualized guest with special
permissions and roles. Just like any
other child/guest, when you open up
Task Manager, you can not see the CPU
usage of the other children on the
Ben Armstrong has a good explanation
of this here:
Lastly, look at RAM usage in your VMs. Look at disk queue length. These will tell you if you need more RAM. It sounds, though, like your VMs just need more total CPU than the host has to give.