WAAS has been available on consumer GPS devices since the mid 2000's and is not "professional" nor does it address reception/interference issus; WAAS provides semi-real-time position refinement data based off drift observed by ground stations within a certain range to compensate for things like atmospheric disruption of the signal. WAAS is built-in to the vast majority of receivers these days.
Multi-band GNSS is what helps address issues around reception like multipath and interference. Receivers used to be pretty expensive, and the number of L5 satellites wasn't that high until the last few years, but now can be found in even a number of consumer electronic devices, and the number of L5 satellites keeps going up (and as more satellites have L5 signals, things will get better.) Several Garmin sport devices have it now, for example. A quick search shows Maxim sells a multi-band GNSS chipset for $10.
There is really no excuse for any autonomous vehicle company to not be at least evaluating multi-band GPS receivers, if only to give more reliable position data in urban environs.
I'd be surprised if at least some aren't using RTK receivers, but this requires a base station within a certain range of the cars, or commercial service (such as that offered to farmers by John Deere.) RTK just isn't that expensive compared to even a single LIDAR unit.
Edit: they can tolerate at least some degree of GPS degradation and use dead reckoning / lidar data in some cases, according to this person: https://news.ycombinator.com/item?id=31940167