Connecting unbalanced parallel battery strings to a common DC bus
Your statements about "precharge circuits" and "switching...in as they equalize" are pretty vague so I can't comment on those.

However, if you connect two batteries of different voltage together then current will flow from the higher voltage to the lower voltage. If you can limit the current then this is just inefficient but not dangerous. If these are lithium batteries then you must limit the current flowing in this case. The current limit must be set at the lesser of the maximum charging current and the maximum dischaarging current. Also note that while current is flowing from one battery to the other there will be less current available for the load.