Hi, technically speaking, this would be a case of pronoun ambiguity, because he has two eligible antecedents: Homer and Marge.
In such cases, the general practice is to split the sentence in terms of the two clauses:
i) Homer told Marge
ii) he ate all of the cake.
Hence, it can be presumed that he (the pronoun-subject of the clause) refers to Homer (the noun-subject of the previous clause). To summarize, a pronoun-subject of a clause can be presumed to refer to noun-subject of the previous clause.
Having said that, there are staggering violations of this in few officially correct questions. Hence, pronoun ambiguity should not be a reason to eliminate any answer choice.
By the way, the above sentence would not really be the best way of articulation, from a tense perspective. The ideal sentence would be:
Homer told Marge that he had eaten all of the cake.
p.s. Our book EducationAisle Sentence Correction Nirvana discusses pronoun ambiguity, its application and examples in significant detail. If someone is interested, PM me your email-id; I can mail the corresponding section.