There are chapter stop extraction utilities that should pull the stops from an existing DVD structure. Whether that will do it in a muxman-compatible format is unknown, but usually they offer some conversion options. Those are not stored in the VOB files, but in the IFO files (I don’t know where, actually, I haven’t messed with DVD’s in a while). Once you have that, there’s a menu option in Muxman to import chapter stops from that export file and then it should just work.
If you have trouble with this, I have GOUT-timed DVD chapter stops in muxman format for the whole trilogy. However, they may not match what’s on the existing DVD5. They’re more-or-less the Blu-ray stops with stops for missing scenes removed. And they are a straight conversion from Blu-ray timecodes, so they might jump to less-than-ideal frames on a telecined DVD (or if my math was bad). If you’re interested, just PM me and I’ll upload them.