A test within the virtual machine is quickly done with the rtl_test.exe utility distributed with RelWithDebInfo.zip file (google). My setup:
- host computer i5 processor Win7 64bit
- guest computer WinXP 32bit
- R820T dongle
My conclusion: unless you accept data loss in your RTLSDR decodes, a VirtualBox virtual machine does not guarantee enough "USB bandwidth" for successful reception within the VM itself.