The energy cost was factored into the CP math I ran - Hemo will generate one more combo point than spamming SS every 12 seconds.
It might also be worth factoring in the very low Energy cost and the fact that not only is it a quick DoT-style debuff which gets consumed quickly (meaning you can lay Hemos as quick as you have Energy in some cases), but it does have a DD portion as well. Also, CP generation will be faster than Combat Rogues but maybe not as quick as SF Rogues.
With good gear SF rogues generate combo points at a slightly higher rate than a rogue spamming SS. However, there are a couple problems. Your critrate against a 63 elite is not what your mouseover + 30% is, regardless of how much we wish it.
So SS rogues generate 1CP every 4 seconds from an empty energy bar.
Seal Fate rogues generate 2CP every 6 seconds (critrate + 30)% of the time, and 1CP (1 - critrate+30) the rest of the time.
My default critrate in raiding gear is ~30%(it's actually 29.6 but 30 is nice and round). Were I to spec Seal Fate this would drop to 25% thanks to the loss of max dagger spec, so I could expect every backstab to give on average approximately (2 * .55) + (1 * .45) = 1.55CP. That's 1.03CP generated per 40 energy vs. 1 for a combat build, but we lose DW spec, precision, and dagger spec, all of which are huge for a raiding build.
Hemo rogues generate 1CP every 35 energy, or 1.75 seconds. So you're generating 1.14 CP per 40 energy, which is much faster than Seal Fate. You'd need to boost your critrate with backstab to 72% - a base 42% critrate - before SF would generate CP faster than hemo.