I think there's one or two service providers who provide import services from vB5 to XF but I have no idea whether they do a double import or whether it's a direct import.
A search through this forum might give the answer:
With double imports, passwords would almost always be lost. We generally only support the password format of the source forum itself. With a double import, the password is either lost initially or it won't be maintained as it's in a different format than what we expect.
This would likely only be resolvable with custom importer changes.