Yep. You can also blend aspartame and AceK (and in fact, that was what Pepsi did with first-generation Pepsi ONE, now reintroduced as "Diet Pepsi with aspartame"), but then you end up with a worse shelf life than aspartame alone.
Basically, aspartame breaks down over time, loses its sweetness, and eventually decays further into formaldehyde. I'm not sure what AceK breaks down into, but its half-life is comparable to aspartame's.
The main advantage of sucralose + AceK over aspartame + aceK is that aceK's taste-neutralization lasts longer than its sweetness. So, with sucralose + aceK, Pepsi can use enough Splenda to maintain acceptable sweetness long after the aceK has started breaking down, and use the aceK purely for taste-neutralization (nobody really minds if it's "too sweet" when fresh). With aspartame + aceK, you still get the flavor-smoothing effect, but after 3-6 months, it tastes almost as bad as pure decayed aspartame.
Tip: if you have diet soda that's ~3 to 12 months old, try adding a packet or two of aspartame or sucralose per 12oz before drinking... assuming you didn't store it in a hot Florida garage (causing more formaldehyde), this trick can resurrect an otherwise-ruined can/bottle of diet soda.