What is the difference between the V+ pin of the MAX232 and that of the MAX3232? The V+ in typical circuit of the MAX3232 is connected to the ground via a capacitor. Can it be connected to the VCC?

For both devices V+ is the output of the voltage doubling charge pump, and the V+ must be bypassed with a reservior capacitor.   The reservior capacitor must be connected between V+ and a low-impedance ground or power node.  If using ceramic non-polarized capacitors it is ok to connect the reservior capacitor either between V+ and ground or between V+ and VCC.   If using polarized capacitors, then the capacitor must only be connected between V+ and ground with the positive terminal connected to V+.