I could see some benefit there as a lot of motocross guys do rowing as well. I do have a rowing machine also which I use for more of the upper body stamina movements currently. There is also this machine which a lot of people seem to talk highly about, although I am not sure it is worth near the cost they are asking, I’ve never used it but it is a similar idea.
Currently I have been trying to keep these two exercises separate, or spend time doing upper body stuff with weight lifting or high intensity timed intervals with weights, etc. Many of the pro moto guys put down some pretty big miles on bikes, usually a lot of their rides are on the longer side and likely a lower intensity, although I have seen videos of riders like Justin Barcia winning crit racers and their trainers claiming “pro” level bike performance. It is hard to know exactly what they are doing though since their coaches keep their training super secretive.