Is the riverside seating wheel chair accessible?

Yes it does

We regularly have guests in wheelchairs dine with us. Take the ramp down at 109 W Narket

Yes! It is wheel chair accessible! Its only tricky getting down to the river. There are a few ramps around. Ask locals for directions because I suck at it. I'll get you lost just explaining it lol

When we ate there, I think there was enough room to get a wheelchair seated at many of the tables. My concern would be if the table was tall enough to allow the wheelchair to get close enough. If you don't have issues with most regular height tables, you should be fine.