In general, the deeper the cycle, the fewer cycles the battery will last. For Nimh, if the state of charge is kept between 20%- 80% there seems to be no practical limit to the number of cycles the battery will last. Most other chemistries are similar. Cell damage tends to occur when the cells are over charged or over-discharged. In a Nimh pack with lots of cells and no BMS, it would be easy for one cell to get weak and be reverse charged during a discharge cycle, destroying it.
Since the best you can get out of regen is way less than 50%, unless you live at the top of a hill, it would be nearly impossible to get a situation where the batteries couldn't absorb the regen charge. To make things idiot proof, you would still need to manage this possibility. You can either stop regen if the batteries get too high, or use some kind of dump load resistor to dissipate the excess. Either of these could be triggered by a BMS circuit if one was present.
Since the best you can get out of regen is way less than 50%, unless you live at the top of a hill, it would be nearly impossible to get a situation where the batteries couldn't absorb the regen charge. To make things idiot proof, you would still need to manage this possibility. You can either stop regen if the batteries get too high, or use some kind of dump load resistor to dissipate the excess. Either of these could be triggered by a BMS circuit if one was present.