Yes, using a pair of dog slickers works very well for carding and blending.
As for is alpaca needs to be carded, it depends!
Is the alpaca raw (straight off the animal) or in a roving form?
Raw alpaca needs to be soaked to get the dirt out. Even if it looks clean, you would be surprised how much dust is on it.
An easy way to clean alpaca is to place the locks in a strainer or netted bag and immerse it in warm soapy water. Do not agitate the alpaca, just let it soak for 15-30 minutes. Repeat with soaking in clear water of the same temperature to remove the soap.
Blot dry and lay flat to dry.
For blending the angora and alpaca, gentle carding is the best way to go.