According to Vaisnava scripture, the sraddha rites may be performed, but the priest performing the rites should be Vaisnavas and the offerings to the pitrs should be Visnu prasada.

The inhabitants of Pitrloka are generally men of the karma kandiya or fruitive activities category, who have been transferred there because of their pious activities.  They can stay there as long as their descendants offer them Visnu prasada.
                                         SB 5:2:2 purport

The shraddha ceremony of oblations to the forefathers should not be performed on ekadasi tithi.  When the tithi of the death anniversary falls on the ekadasi day, the shraddha ceremony should be held not on ekadasi but on the next day.
                                         SB7:14:23 purport