Does the garbage disposal need to vent if is connected to a dishwasher?

If your garbage disposal is connected to your sink drain and your sink drains OK then it should already be vented if you dishwasher is not draining check to see if the knockout inside where the dishwasher drain is connected to the garbage disposal. There is a plastic knockout inside the garbage disposal at this point

Disposers are not vented temselves but the sewer line they drain to needs to be vented. Maybe we are mixing some terms here, is this what you need to know?

If you mean the vent that is on the sink, where the sprayer usually goes, I think it is a drain not a vent and no I don't think you need that. I don't have one, it drains to the dishwasher instead. You would need it if you didn't have a garbage disposal. Or am I totally misunderstanding this.

Sorry, I meant the dishwasher drains directly to the garbage disposal so you don't need that drain on the sink.

I misread the original question when I saw the word vent. You mean a dishwasher air gap. You need a air gap or a high loop in the drain line almost to the flood rim of the sink. You must have one or the other to avoid back siphoning of the drain water into the washer. Most city codes will tell you if you must have one, the loop works as good in my book.