It is not recommend but people do drive that way, so you will be fine.
And if you have PVH(pulse vacuum hubs, 1998-2000) then they probably were not engaged anyway.
If you need 4WD then these need to be changed to Rugged Ridge manual hubs, you can't rely on PVH hubs to work when you need them.
The Borg Warner 1354e transfer case(what a '99 Ranger has) doesn't have a way to allow both drive lines to spin at different speeds like All Wheel Drive transfer cases do(a clutch or viscous coupling).
But if your tires are all the same size it won't stress the transfer case that much.
If you think about it, when there is snow on the ground and you were in 4WD and the axles did spin at different speed you would be sliding all over the place, because wheels would be turning at different speeds.
That doesn't happen, well hopefully, so don't stress about it.
Sometimes you do need to back up to get transfer case and PVH hubs back into 2WD, after driving in 4WD for any distance, dry or on snow