Are there any hidden advantages that I don't see in using DPP?
It depends on whether or not you believe the 'Canon marketing pitch.' :-) The pitch is essentially that because Canon makes the software and the hardware, their RAW processing is better than the competitors will be. Having done side-by-side comparisons I can say this... In straight apples-to-apples RAW comparison (e.g. all settings the same) DPP RAW processing produces an initial output that is slightly more contrasty by default. Is the output so much better than Aperture that it warrants a change? Are there hidden advantages to DPP? Well, I have two answers:
Answer 1: For me, the answer was 'not it isn't, and no there aren't.' I could slightly tweak my default processing settings in Aperture and get images that were indistinguishable from those made in DPP (unless, perhaps, you're a 'pixel peeper'). The difference was not worth changing up my workflow (and in the 'workflow' department, Aperture has DPP beat in spades).
Answer 2: Since DPP is free, and you already own Aperture, it wouldn't take more than installing DPP and doing some side-by-sides. I didn't see enough of a difference to warrant the change, but maybe you will? Just a thought if you're still on the fence after my first answer. :-)
In general my experience with Aperture is that it has better asset management, more features, and a better workflow through the product... But I to have to acknowledge that my feelings of a 'more intuitive' workflow may simply be due to my familiarity with Aperture, and relative lack thereof with DPP.
In many ways to me DPP felt like a 'lite' product, and Aperture was the 'full' version (as much as that comparison can be made for 2 different pieces of software from 2 different companies). The bottom line for me was that DPP wasn't a bad product at all, but it didn't offer enough of a difference or improvement to warrant shaking up my whole workflow over. But again I will say that if you still find yourself on the fence after my 'thumbnail opinion/review,' the good news is that it's free (except for the hour or two it will take to install it and play with it a bit) in order to test DPP out and see for yourself if it is better enough for you to be worth making a change...