Migrating a VM with VMware is easy, from a Workstation to vSphere cluster it can be done with a VMware Converter.
I have little experience with Hyper-V though. There is a VM on a Hyper-V on Windows 8.1 and I have to move it to a Hyper-V Cluster.
How can I do it? Is there a tool like Hyper-V Converter
or should I just move the VHD and recreate the VM on the Hyper-V cluster?
There are excellent V2V Converters like ones StarWind and 5nine do but in your case you only need to a) export and b) import VM. See link below.
Overview of exporting and importing a virtual machine (TechNet)
Export the VM. Import it on the new machine. You'll probably have to specify a few things like the network switch when you import.