To a possible extent, adiyen was contributing to Thanjavur, Raja Matam Santhana Rajagopala Svami temple`s kainkaryam. Recently adiyen got to know that a sanctum for Pillaiyar available at that temple after which adiyen stop contributing. I also learned that adiyen’s money was used for kainkaryam of that Pillaiyar. As result, will adiyen be considered to be tainted with the association of demi-gods?

There is no taint of getting associated with a demi-god in this instance, as the act was not intentional.
To a similar query in the previous issue of Sudarshanam, we had said that when one is asked for contributions to build temples for demi-gods, one can treat this as one among many expenses.
As you were not asked specifically to contribute for the kainkaryam of a demi-god and as you had not contributed specifically for that demi-god, no taint will result.