I did something like this years ago.
As I recall, I connected VHS recorder and DVD recorder to TV (using SCARTs). I probably played backed the VHS to the TV and then picked up the output from the TV via the TV's other SCART socket and recorded this on the DVD. There might have been some degredation in quality, but not seriously noticeable (as all looks poor by today's standards).
Of course, problem (as much as anything) today might be finding a TV with two SCART sockets.