Hello pascalvz88,
I assume here that you are using a B-Station, and that you are using the internal FX-generator. The answers is yes, but only when the fixture itself supports it. The B-Station knows 2 different types of dimmers. The, so called, virtual dimmer and a dimmer implemented within a fixture (a personality including an 'I' channel). The difference is that in the former case the 'dimming value' is reflected in the actual colour channels whereas the latter reflects this in the intensity channel going to the fixture.
Unfortunately, it is not possible to use a FX in combination with a virtual dimmer. It is possible to use this in combination with fixtures implementing an intensity channel.
Hope this answers your question.
Best regards,
Jurrien