Well if they have VNAV engaged that will take care of the vertical profile according to the FMC, if you want to climb manually which the CRJ and ERJ do alot, you would engage a speed and then the VS speeds would show up.

Yeah, VNAV will take care of the vertical profile AND the speed aswell. So generally both IAS and V/S boxes are blanked when flying VNAV, unless crew has manually entered a different crz speed.

As a rule of thumb, the V/S mode is used mostly below 10.000ft in descents. for many reasons, I might add.
The primary reason is to fly the aircraft "heads up". By that means no FMC fiddling (which VNAV requires to be setup properly) and instead using the MCP (autopilot panel). 95% of the descent and approach planning should be conducted at cruise altitude they say  8)

If you want to use VNAV in descent (in TMA's or CTR, where traffic is tight), elect VNAV SPEED, instead of PTH (path) since VNAV PTH may exceed flap speeds when high and diving for the path.