Questions About Charging Lithum Ion Batteries
Q1) Can you use BMS and charger at the same time. 

Well it is not clear what you mean by a smart charger. If it is a bulk charger (i.e. just two wires connecting to the battery's bulk voltage) then you for sure want to use the charger in series with the BMS. The BMS is what is going to open circuit the charging line when one of the cells reaches 4.2v. 

If it is a balance charger, (i.e. in addition to the two bulk wires there are a bunch of small wires/balance leads also connecting the charger to the battery) well you can still charge it with the BMS on there. You will need redundant balance leads though, or partially disconnect the BMS. But I am betting you have just a regular bulk charger. 

Q2. Charger specs. 

The charger is likely speced for a 52v battery. If you test the output it will probably go up to 58.8 ish volts. That would just be the nominal rating most likely. 

Regarding the current: If the charger is rated to deliver 3amps, and you are hooking it up to a pack that is 14s x 1p (one cell in parallel only) then you will but charging the cells too fast really. The cells might be able to take it (check the datasheet for max charging rate) but there is a direct relationship between rate of charge and rate of wear on the battery. If you charge that fast, even if your battery can take it without failing you can expect your batteries to wear out quicker.