It is possible to call a SAS proc (e.g.: proc corr) from a function defined in proc ga using the dusubl() function.
First you will need to create the input data source of proc corr, then call procc corr using dosubl(), then read the results from the created dataset (open(), read(),... functions).
If this is realy just calculating correlation and data is already in variables of proc ga, I would write the calculation myself.