I have discussed Vyāḍi’s position here and mentioned some basic criteria for distinguishing references to his position and to the apoha one.
The first criterion is that the discussion has to refer exclusion (nivrtti) or difference (bheda) as the sentence-meaning, since Vyāḍi was convinced that words meant individuals (dravya), vs. the apohavadins, who maintained that exclusion is the meaning of both words and sentences. A further element in favour of the attribution to Vyāḍi could be the presence of his chief opponent in the Mahābhāṣya, i.e., Vājapyāyana, or his view, that words mean universals (jati) and sentences mean a complex (samsarga) of word-meanings.

In the case of Jayanta’s NM 5, a further element would be the presence of Vyāḍi’s view among the ones he previously discussed within the discussion about the nature of word-meaning.

The first two criteria are seemingly fulfilled, although the identification of No. 2 with Vājapyāyana’s position has some weak points (since Vājapyāyana’s position in regard to word meanings does not amount to direct realism) and basically depends on the identification of No. 3 with Vyāḍi’s position. As for the third criterion, the discussion about the word meaning at the beginning of NM 5 is differently shaped as that of sentence meaning, with the Naiyāyika siddhānta coming first and then the beginning of a general discussion about whether the words mean an individual, a universal or a configuration (ākṛti) (Mysore edition, pp. 5–6). The first two alternatives could refer to Vājapyāyana and Vyāḍi, but also to many other authors, since the dilemma has been a hot topic in Indian reflections about language ever after the two grammarians.

What are we then left with, in order to decide concerning Vyāḍi’s presence or absence in NM 5?

Apart from external factors, such as the presence or absence of Vyāḍi in other authors of the same era (about which Kumārila and Pārthasārathi will be very significant, see here and stay tuned for further posts), we may look at Jayanta’s way of discussing it and at the sequence of the discussion of these theses in NM 5.

As for the latter point, the portion of NM 5 dealing with the sentence meaning is basically a discussion of the Mīmāṃsā positions on it. The other theses are dealt with briefly within the the initial discussion on what is the principal element in a sentence (in the first 11 pages of the section). The apoha theory is not dealt with again, possibly because Jayanta has dealt with it extensively while discussing the word meaning, at the beginning of NM 5 (see Kataoka 2008 and 2009).

As for the former point, at one of the last pages of NM 5, Jayanta goes back to the topic and discusses again saṃsarga and bheda. Here, the two terms are back again, and Jayanta concludes by saying that

The exclusion of all other [word meanings] is not the meaning of a word. Therefore, the meaning of a sentence is not difference (anyāpohas tu na padārtha ity uktam. tasmān na bhedo vākyārthaḥ, Mysore, p. 138).

Thus, he at least connects the apoha theory of word meanings with the theory of sentence-meaning as difference and refutes the latter because the former has been refuted. In this sense, what he refutes is no longer Vyāḍi’s view, given that for Vyāḍi words mean individuals and not exclusion of any other word meanings.

On Vyāḍi and apoha, see this post. On apoha in Jayanta, see this post.