Yes, seam welding wheels can be dressed on the machine. On some machines the wheels are driven by knurled drive wheels that drive and also maintain the shape of the wheel at the same time. The photo below shows a knurl drive system. The wheels are continually driven and dressed each revolution.
Seam Welder with knurled drive wheels
On a machine with a driven central hub a system with a dressing wheel similar to the one shown above could be used to dress the wheels at the proper interval between parts. The dressing wheel would no longer drive the wheels. It would only come in contact when desired. An external secondary system would move the dresser or dressers into the proper position to dress either each wheel or both at once, if placed between the wheels. This would be very similar to a robot indexing to a dressing station to dress spot welding electrodes every so many welds.