Suntour derailleur compatibility with shimano shifter

This is going to come down to the cable pull ratio: that is, how far the derailleur moves sideways for a given cable pull from the shifter.

Suntour hasn't made derailleurs for decades, so it will be hard to find experiences using them documented online. Based on this discussion, I would not be optimistic. The cassette (or possibly freewheel in this case) will only complicate matters further, since the distance between sprockets will also determine how well your setup shifts.

All derailleurs do not behave exactly the same way. Why should they? Suntour requires a different amount of cable pull compared to Shimano to move the same amount of lateral distance across the cogset. Specifically, Shimano derailleurs require about 10% more cable travel to achieve the same amount of movement across the cogset than Accushift. So the mixed marriage of Suntour and Shimano may sort-of work over 5 cogs or so, but eventually the cumulative error at the ends of the cogset will cause sloppy shifting.