A stepper driven indexer is available as a stand alone system. I have run one on a small Webb CNC 3 axis knee mill. It had two basic modes of operation. You could set up the tool with all the parameters for the operation for that tool, execute an index move and the indexer would stop. Then the CNC control would go through all the code for that feature, whether it had one tool or ten. Once the program was finished for that particular feature, and homed out, you I would hit the "index" cycle start button on the separate control for the indexer, which would move to the next position. Cycle start the main control and repeat all tool operations on the next identical feature. Repeat as necessary. The control for the indexer was separate from the CNC controller for the mill. It was more of an accessory. It worked very well, within its limits.
As I recall, there was the facility to link the two so that the end of cycle on the main control could trigger an index move, so the entire part could be done without operator intervention. It's just that you could not program a feedrate into the indexer. It was wide open speed or nothing. and like I said, no way to connect the to to coordinate the start/stop between the indexer and the other axes.
Remember though, that was a while ago, and only one make of indexer, but that's how they are all designed to work, as far as I know. I have seen people set up repetitive hole drilling jobs even on manual machines like Bridgeport mills with a microswitch at the top of the quill so that after each hole was drilled, manually, the indexer would move to the next hole location. I think basically, the understanding is that they are intended to move to a new position rather than cut along the way to the next programmed position.
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