Is it possible to solve VRP using OR-Tools CpModel, instead of RoutingModel? I want to do synchronized VRP, which is combining vehicle routing and scheduling constraints
The answer is yes. Is it worthwhile ? it depends.
If you just want to have two persons visit the same virtual place (2 duplicated nodes) at the same time, you can force the time cumul var to be equal when using the routing library.
This will probably more efficient than the CP-SAT VRP code as the routing library is highly tuned.
If you want more complex constraints, you can try CP-SAT. You can look at ortools/constraint_solver/routing_sat.cc to get some ideas.