Random effects model in stata - how sensitive to non parametric assumptions

I am using a random effects model to analyse a 4 point time series longitudinal data to compare the effects of an intervention and control, some of my independent variables are non-parametrically distributed - how sensitive is random effects model to this? can i use it or should i perform a different test?

Also what is the best way to right up results? Reproduce the table or pull out certain stats?

many many thanks