I have not brewed this, and I have no official source saying you have to rack to a secondary, but in my experience it is always best to rack to a secondary before adding anything else to the beer. I have made a summer shandy recipe and a blackberry wheat recipe that had additions to the secondary. I found that by racking off the yeast cake before adding more "stuff" to your beer, you get a cleaner beer when it is time to carb/condition the beer. Again though, this is purely my opinion and not a brewing fact. Hope it helps, let me know how this beer turns out, sounds good!
Next Up: Winter Ale (Snow Cap Clone)
Fermenting: Pumpkin Ale; Oktoberfest
Conditioning: Oatmeal Stout;Barleywine; White IPA
Bottled: Belgian Wit; Island Pale Ale; Mac & Jacks Clone; Temptation Ale; Not Your Ordinary Irish Red; Summer Shandy