I can say with quite a bit of confidence that the S5PC110 Hummingbird is not inside the Apple A4. Hummingbird has a single-channel memory controller, so the Samsung S5L8930 in the A4 is probably a modified version of Hummingbird’s sister chip, the S5PV210, which has a dual-channel memory controller like we know the A4 has.
I’ve seen more and more people saying that Hummingbird is in the A4, and it’s just more uninformed speculation that tends to proliferate. While it’s possible in theory, Hummingbird was designed for smartphones while the S5PV210 was designed specifically for tablets and MIDs, and thus S5PV210 would be the obvious choice to use. They were both introduced last year together in this press release, which has some more info about S5PV210:
Intrinsity has worked for Samsung as well as Apple, though I personally believe that it was PA Semi (which Apple acquired last year) that modified the S5PV210 into the S5L8930 for the A4, simply because on June 10th 2008, Steve Jobs told the WDC that he was having PA Semi work on chips for iPhones and iPods (and we all know that really, the iPad is just a big iPod!)