No, Murmur3 *is* busted. Some clever people have found a way to perform a universal multicollision attack, that's a key independent attack. An attacker doesn't need to know the seed for an attack.

Collision counting as not a solution for the issue, just a workaround. It has been proofed for decades that a tree data structure is not vulnerable to this kind of collision attacks. A hash function with crypto properties is the second best solution.