How many dogs spawn with the attack dog killstreak? Is there a set amount, or do they just spawn for X seconds?
The dogs spawn for ~60 seconds continuously. There tends to only be 4-5 dogs active at once, but when one dies another replaces it by jumping into the map somewhere else.
However, the dog mechanic is quite a bit different in Black-ops then it was in World at War. Because dogs are harder to get (11 kill streak instead of 7) they now kill in 1 bite. But instead of immediately 'knowing' the location of enemies dogs are now attracted to gunfire, making them much easier to avoid