Welcome !

In general, I would say the connection is feasible in two hours, as I've always moved quite quickly around the airport for the few flights i've taken in dar. I would say the main risk you have is your flight arriving late - in which case you might need to run, which might be stressful if the two flights are not on the same ticket.

I took the 7pm flight to JRO in may (i.e the end of low season), and paid around 50 dollars for the one-hour transfer to Arusha. I can recommend a driver if you want.