Protein can cause a spike in Insulin, but not aspartame[6]. Furthermore, consuming aspartame with or without carbohydrates resulted in aspartame not contributing to an insulin spike[7].
Diabetics were found to have no spike in insulin after ingesting nonnutritive sweeteners[8]. Swishing a solution in the mouth had no effect[9]
About the only study suggesting sweeteners could spike insulin was found in vitro rat pancreatic cells when coupled with glucose and done with direction transfusion (instead of ingested orally)[10]
the data from extensive in vivo studies in human subjects show that low-energy sweeteners do not have any of the adverse effects predicted by in vitro, in situ or knockout studies in animals. [11]