I'm one of Indago developers. Glad to hear you are using it.

Currently Indago only supports continuous optimization (continuous variables). However, your rounding workaround is legit and not so far from Discrete PSO method. However, methods like GA are more suitable for discrete optimization since it is intrinsic to their fundamental idea.

We plan to implement some methods and support discrete or even mixed problems in the future. But not in the near future :)