If we are talking about a plug-in battery pack sure it will do (yet its more expensive than other solutions)... if we are talking about a solution for a built-in battery-pack + charger/protection circuit i am not so sure.... not about its functionality or results but about its practicality...
The OP wants to build a 3S LiPo. He appears to want to build a charger for it using 3x single cell chargers.
He could charge the cells individually. They would need to be wired correctly/unorthodox-ly However you cannot use the balance charge input (if one was wired) to charge the cells individually. They are wired in part-series.
Cell 1: 4.2V (Cell 1 only)
Cell 2: 8.4V (Cells 1 and 2)
Cell 3: 12.6V (Cells 1, 2 and 3)
A balance charger is able to derive the individual cell voltages by basic subtraction and modify each charge voltage/current accordingly. But you can see you can't use a 4.2V charger circuit to charge individual cells (except cell 1) using a normally wired balance charge lead.
The question would be.. if the balance lead was connected directly to each cell, so for 3S you would have 6 wires. How would the cells being wired in series for the output effect the results.
If the aim is to be able to create a 3S Lipo capable of being charged from a USB plug, as part of a product, then that's different.
As to lead acid versus LiPo charging the only difference that I am aware of if that LiPos use a peak voltage, min current cut out, where as Lead Acid chargers usually carry on with a trickle charge mode.