An Onain is not obligated to do Mitzvos Asei. An Onain does not Daven, nor make Brachos. Suppose a person is an Onain, and that day is his father's or mother's Yahrzheit, does he say Kaddish for them? (sources)
See the Kitzur Shulchan Aruch 196:9; "an Onain says Kaddish if he has Yahrzeit for a parent, or is in his "11 months" Availut for them". But he seems to be referring to Shabbat.
In 26:12 he says that one who could not say Kaddish during the day - for whatever reason - can say Kaddish for a Yarzeit the evening after.