Do you know what brand of DVD recorder he's using? I ask this because the Panasonic recorders have a time-base corrector on their inputs which does a pretty job of fixing this kind of problem. By that I mean that any problem on the source tape does not cause a WORSE problem on the resulting DVD.
I've transferred a bunch of old Betamax tapes that have tons of breakup between segments, and the Panasonic recorders take it stride. Yes, the breakup is still on the DVD, but it doesn't cause any problems like you described.
That said, there are plenty of external TBCs out there, but I don't any experience with anything other than multi-kilobuck professional units, so I don't know how well they work.
One other possibility would be to play the source tapes in a machine that has a built-in TBC, like some of the recent vintage JVC S-VHS machines. That will keep loss of sync, etc. from reaching the DVD recorder.