Transfomer on a speed controller output

[hrc]

Just was thinking...I saw where a 230 3phase motor was being driven from a AB speed controller, but attached to the motor wiring (via a jbox) was a transformer to run an exhaust fan.

I asked the guy putting it in, he shrugged and said it was how it was designed but I wonder how the transformer (and fan) will react over long term to the VFD output.

Comments?