the alimony is deducted on tax return, so it is not included in the adjusted gross income. Since completely unrelated person gets it, this amount should not be considered available for paying for youe college.
I am not 100% sure, but I am about 99% sure that the alimony amount in your particular situation will not be added back to adjusted gross income on CSS profile or FAFSA.
So, if your dad makes 150K and pays 20K to your ex-step mother, than it will appear to colleges that only $130K are available to your family. I know it is still high, but sometimes every little bit helps.