The reason you need to use a LiPo charger has nothing to do with trickle. The reason is that a NiCAD/NIMH charger charges at a constant rate until the battery voltage peaks, then begins to drop off. At that point, the charger will STOP quick charging. Some chargers will then trickle, some won't.
THe problem is that a LiPO pack does NOT reach a peak voltage and then begin to drop, so a NiCAD/NIMH charger will NEVER be able to detect that the LiPO is full. As the LiPO pack reaches full charge, the voltage will continue to climb and the charger will happily keep cranking the juice to it even as the LiPO gets hotter and hotter until a catastrophic failure happens.
A LiPO charger will charge at a constant current until the pack voltage reaches 4.2V per cell, then switch from a constant current to a constant VOLTAGE charge. Once this takes place, the charge current is slowly tapering off. The charger watches the voltage of the pack, and tapers the current off to keep the voltage at 4.2V per cell. Once the current gets to a predetermined level, the charger considers the pack full, and stops.
To answer the original question in this thread...
Yes, you CAN use a LiION charger to charge a LiPO, but you will not get a completely full charge. LiION batteries are charged in the same manneer as LiPO, but the LiIOJN chemistry reches full charge at a slightly lower voltage. Chargers for LiION batteriesd will safely charge a LiPO, but to the slightly lower voltage of a LiION, which is about 90-95% full for a LiPO.
You wouldn't want to charge a LiION pack with a LiPO charger, the higher voltage of the LiPO charge would overcharge a LiION. YOu might get away with it, but you'd be overcharging and reducing the life of the pack. You'd also be inviting the possibility of a thremal runaway at some point. It probably wouldnt' go that far, but the possibility is there.