Thanks for your reference times in the comments. This is the coro/guía (or montuno) section where the lead singer trades phrases with the chorus. It is an 8 bar progression but there is no D♭. Here is the progression:
||: B♭m7 |B♭m6 |Fmaj7 F6 |Am7 D7 |Gm7 |C7 |Fmaj7 F6 |Cm7 F7 :||
In the first bar the pianist is actually playing the notes of a D♭ triad in his tumbao (also called a montuno), rhythmically alternating the A♭ by itself with the D♭ and F together. The thing to keep in mind is that in this style of music when playing tumbao the pianist does not play the roots of the chords, he plays lines that carry the voice leading of the harmony (7-3, 7-6, 5-6, etc.) The bassist is in charge of playing the roots of the chords and he is playing B♭. B♭ under a D♭ triad is a B♭m7.
As a side note the term montuno has 2 different meanings. It can refer to the rhythmic syncopated part the pianist plays. It also is the name of the section of the song where the lead singer trades with the chorus. That’s why I and many others who play this style like to call it “coro/guía”, translation: chorus/guide.
Tumbao originally meant the part played by the bass but nowadays it has evolved to refer to both the bass and piano part.
I should have mentioned, what a great song, arrangement and performance! The arrangement sounds like it might have even written by Jose Febles, the greatest arranger in that style from that era in my book.