Careful. The 5 spoke Marchisini's on the S4 are 2 lb lighter each than the 3-spoke on the other Monsters, which implies some differences in construction. They may not be a straight substitution necessarily. I'd ask someone who is knowledgeable on Ducati wheel assemblies.
the s4 rear wheel has a 25mm axle... you'd probably have to at least swap the bearings and bearing spacer to fit it to m900's and 900ss's that have the 20mm rear axles. bearings are easy to find but the spacer might be more difficult to scrummage up even if simple to make.