Sure, but it's not a good benchmark. If you can demonstrate that you have blazing fast performance, but only for the exact input data that the benchmark uses, then you haven't demonstrated anything at all beyond an ability to tailor your code to a very specific input. But in the real world, we don't get to write our code for a very specific input (after all, if we knew what the input was ahead of time, we could just pre-calculate the answers instead of publishing the program).

So yeah, if you can come up with a tailored hash algorithm that works correctly and is DoS-immune for all possible input for the program, go ahead and use that tailored hash algorithm. But if your hash algorithm is only correct for the specific input data the benchmark game uses, and would not be collision-resistant under real world conditions, then you really shouldn't use that hash as it does not demonstrate anything useful.