can you take a side by side on trails

Some yes but not all

The scenic loop at red rock canyon is not much for a hike (flat dry wilderness) but more of a scenic drive through.

Yes

Motorcycle? Only around the main loop. Others are foot trails. Stroller? Many trails are rough and uneven. Not meant for carriage.

Sure can

I've never seen a side by side at the R.R. itself so I don't think one is allowed to ride one in there but there are few other desert trails around the area with no restrictions.

The starting portions of a few trails are wider and could accommodate a side by side stroller that can handle going on dirt until you reached the parts where it starts to climb the mountain. In general, the trails are not particularly stroller friendly.