Did the DC-9 ever use RATO in revenue service?
The JATO/RATO retrofits were used only by Overseas National (later National Airways) when operating out of hot/high airfields for military contracts. They were never used as passenger flights, but you could say that these were "revenue" flights as they were done for monetary compensation.

I can't find any history on ALM980, only that it was registered as N935F and operated by Overseas National as a passenger flight. N935F does not show any history in the FAA registry other than it being reserved. It is possible that this was a converted cargo aircraft.

Here is a picture of an Overseas National flight using the JATO rockets:


Source: UT Dallas

It should be noted that the DC9 was not the only passenger type aircraft to get the "JATO" treatment. Boeing modified the 727 to operate out of short fields by adding JATO rockets. Aviation Week did an article featuring the DC-9 JATO modifications:


Source: Aviation Week (article paywall)

The magazine cover linked above shows a DC-9 take-off (an Overseas National flight).