Yes, it is; even the official documentation mentions it (and recommends you disable Hyper-V) and it is FAQ #1 in the support website. One of the reasons mentio

Yes, it is; even the official documentation mentions it (and recommends you disable Hyper-V) and it is FAQ #1 in the support website. One of the reasons mentioned is that VirtualBox runs (some) emulated devices in kernel space but is not allowed to do when running with Hyper-V. The official API forces custom devices to strictly be user space, and only some basic hardcoded devices are emulated from kernel space. The "secret sauce" of a desktop virtualizer is in part in the selection of devices it emulates, so this severely cripples VirtualBox.