That depends...
If your head only goes to the tank, and if you don't have a problem with the tank contents flowing back down the head discharge line into the toilet when you're heeled, you don't need a loop. If backflow is a concern, I'd put one in. I'm not sure what you consider "the space provided," but on most boats there's plenty of room on the bulkhead above/behind the toilet, which is where a vented loop belongs, not buried below decks somewhere. And while we're on the subject...if you have a manual toilet that's below--or even a good portion of the bowl--the waterline, you really should put a vented loop in your head intake. Relying on the dry/flush valve in the toilet is a good way to sink a boat in its slip. The loop goes between the pump and the bowl, at least 8-12" above the waterline at angle of heel.
