It really does. More than just the light colored orbs floating around.
I've had 2 of my friends manage to get Morde and each time they used their ult, I didn't even realize they ulted someone. They just disappeared, and when you're in the middle of a team fight and suddenly your teammates icon disappears from the mini map you don't automatically think, "oh cool they just ulted."
It also feels extremely out of place that they just poof out of existence until the ult ends with no particle other than light colored orbs on the ground. Especially since it's an ult that can last up to 7 seconds depending.
It doesn't even need a super flashy particle. It could be something similar to Kayn's ult particle when he jumps into someone, or even a darker/different colored and slowed down flash-like particle. Just something that isn't just him and the enemy poofing out of existence.