Thanks for giving us an update. Your husbands counts are all on the low side, but not drastically low. He'll be safer as his platelet count increases. I think that going from AML M2 to stable counts in a year is a success story. Congratulations.
Some people would have trouble exercising with below-normal hemoglobin, so it's great that your husband can exercise regularly. Exercise doesn't directly improve blood counts (in fact it temporarily consumes the oxygen that hemoglobin is carrying around your body) but it helps the body in many other ways that improve overall health.
I've read advice about exercising with low platelets (
here is an example) and they almost always focus on precautions for people with extremely low platelets, such as below 50. For someone with platelets of 115, the cautions aren't as severe, but it would still be wise to avoid activities that leave you banged up. A workout at home or in a gym is a lot safer than contact sports!