At first glance, I thought it could be dangerous to use multiple smart chargers because they could get into different states, but after thinking through all the possible combinations, I've convinced myself it is actually safe -- provided the total current is less than what the batteries can accept.  It might not produce the optimal results for your battery lifespan, though: they could transition from bulk to acceptance or acceptance to float before the battery is actually ready, because each charger can only sense its own contribution to the charge current.  Chargers in different stages shouldn't fight each other directly because they sense the current/voltage of the system.  Floating at different voltages should be safe; the charger with the lower float voltage would just not be doing anything.  If one or more chargers has a float voltage above that which the batteries are designed to handle, that would be bad... but that's also bad with just one charger.