Yes, although increasing processing time will increase the latency as well. I’d be more concerned about latency than about CPU usage also, but if you’re operating at large volume then overall processor utilization is relevant (but probably that’s extremely rare for games).
I’d be curious to see how much of an actual impact it has on package latency. By the time you send a packet over the Internet, you’re already looking at a time to reach destination numbering well into the tens of milliseconds and easily reaching over 100, and that number can vary significantly in between packets depending on the connection quality. All that considered, I’d guess that encryption latency would be lost in the noise - but I’d like to hear anyone who’s tried it weigh in. Regardless, I agree that it never really makes sense to encrypt real time traffic. No point in doing superfluous work needlessly.