A lot is possible, but it depends on the level of fidelity you want to reach, and that should answer your "Should I ? " question.
If you are looking to simulate the whole system, maybe because you want to improve the Controller on your PMSM, then yes you should consider this.
But you may want to simplify the forces of the fluid on the impeller. If you can find a simple enough equation that you can represent with MATLAB or Simulink, than it becomes feasible.
You can take a first look to a very similar model here:
this would be a great way to get an overview as a starting point, although it is a simpler system to model (no impeller with blades).
Step 1: importing your CAD
In your case if you are using a CAD software compatible with Simscape Multibody Link, you need to setup the CAD correctly, building it up with the right constraint in order to allow for rotation of the shaft. So you need to do CAD with the dynamics in mind. Then you can import it and move it in multibody correctly.
If you plan to import single files of the CAD by yourself, you need then to use a Filesolid block to see them in Multibody and recreate the assembly manually with Multibody joints. It should be failry straightforward for a pump, you basically have two pieces (housing and Shaft/impeller)
Step 2: connecting Simscape 1D (eg Simscape Electrical or Fluids) to Simscape Multibody:
Use the Simscape Multiphysics Library on file exchange for examples.
There are example of moving a linear actuator using electric motor or hydraulic system. You basically need to create a dynamic forces loop to transmit 1D effect to 3D and get back reactions forces.
Step 3: Create a water force model to apply force to the impeller.
This is not the easiest step, depending on the fidelity you want. You can apply forces to a certain frame placed on a multibody solid using the "External Force and Torque" block. You can "discretize" the impeller by creating 3 or 4 frames for each blade (I would start with 1 per blade). Then you can measure the position of the blade using a Transform Sensor in Multibody. Depending on the position of the blade, you apply a certain force due to water to the various blades in a different way depending on how you model it. The forces of the water can be calculated with a mix of Simulink and Simscape Fluids to represent the water circuit. That will impact the rotation of the shaft and allow you to tune the controller of the motor.
So a lot can be done, but it depends on how and which question you want to answer. If you are looking to improve PMSM controller before a physical test, and you know how to simplify the water model of the forces on the impeller go for it.
If you are looking to calculate fluiddynamic efficiency or structural properties of the impeller, this is not an answer Multibody can give. You need either FEM/CFD software.
Hope this helps