I downloaded both the Uber and Lyft apps here in NZ and used them both happily the whole time I was in the States. I always compared prices before ordering and 9 times out of 10, found Lyft to be cheaper.
My phone company has special roaming packages which I prepaid before I went and found useful.
You could just order a Lyft with wifi, but being connected to internet throughout the whole journey is useful as it allows you to track your route and apply an instant grading (and tip should you choose) at the end of the journey. Also, the apps will sometimes suggest you walk a few metres from the ordering point to a meeting point, and if you loose wifi in that distance, you won’t be able to track when the car is arriving.
So in short, having some form of roaming is not essential, but definitely useful.