Wandering traders and trader llamas does not have same spawning rules as animals, but they can affect the mob cap.
Steps to reproduce
Create a void superflat world
Press F3
Summon the wandering trader and trader llama
Observe the mob cap (C:*)
❌ → The passive mob cap is increased.
Observed result:
The wandering traders and trader llamas does not affect the mob cap.
Expected result
The wandering traders and trader llamas can affect the mob cap.
Can you please provide more information to the report? You can do that by adding the how to reproduce steps if it can be reproduced.
Update: Can confirm.