the openrouteservice is a route calculation tool.
It takes exactly two coordinates and a means of transportation and calculates the best route between them.
VROOM, on the other hand, solves the vehicle routing problem. That mean, given a fleet of vehicles and some job sites with known times between each locations (and possibly job and time constraints on vehicles and job sites) it calculates how to best serve all given job sites.
With this in mind, the ors complements VROOM such that it provides the numbers that vroom assumes to be known.
Thus, if you have any optimization problem with more than one vehicle or more than one job site or any constraints on vehicles and job sites, VROOM is what you’re looking for.
If you only want an answer to the question “What’s the fastest route from A to B”, you’re looking for the ors.
Hope that clears things up,