Ok, frenzy is a ''haste style effect'' meaning it does not stack with other ''haste style effects'' such as a speed weapon, the haste spell, righteous wrath of the faithful, and so on.
whirling frenzy is a flurry style effect, giving -2 to alll attacks in exchange for another attack, it is vastly different from a ''haste style effect''.
The two stack, and it's pretty obvious they do.