Actually, there is no inconsistency in the two Wikipedia articles you gave the links to.
The vowels [ɑ], [ŭə], [ŏə], and [ĕə] are written with the help of a special diacritic sign called bântăk (a small vertical line written over the final consonant of a syllable, ់).
in a syllable with inherent [ɑː] without any diacritical vowel symbols, bantak shortens the vowel to [ɑ], UN transcription á.
in a syllable with inherent ô, the vowel is modified to [u] before a final labial, otherwise usually to [ŭə]; UN transcription ó.
in a syllable with the a dependent vowel symbol (ា) in the o-series, the vowel is modified to [ŏə], UN transcription oă, or to [ĕə] eă before k, ng, h.
As for [ɔə], to write it another diacritic sign is used, sanhyoŭk sannha (័), its o-series pronunciation becomes [ɔə] before final (silent) r.
All this is written just in the next section of your Wiki article. See also this section of the same article.
And specially for you here is the book @neubau refers to, complete and downoadable for free, it is the ultimate and precious guide to the Cambodian system of writing which is probably the most complicated among the phonetic writing systems of the world. Please, read the sections that begin at pages 8, 24, and especially 47.