Does increasing the number of cores result in the increase in the number of interrupts that can be handled by that processor ?
Hardware-wise, since the two processors may even share hardware components such as RAM, my guess would be that more synchronization would be required between them, so more interrupts would occur than in a mono-CPU system. So the hardware answer would be: NO.
Software-wise, once the interrupt went into the operating system (which are all multi-threaded now), it should be able to pass its handling to a thread running on the other CPU and then handle new incoming interrupts. So the software answer would be: YES.
The simple answer is yes. Any core can handle an interrupt and if the OS is clever and supported by a decent interrupt controller two cores would allow you to handle twice as many interrupts as a single core. Depending on the system and type of load it may make sense to have one core handle all the interrupts or to spread them out among all the cores.
Caveat : This would be true of a multicore system such as the Intel x86 ones where each core has its own APIC. There might be multicore systems where interrupts are handled differently (such as a dedicated core handling all interrupts) where the capacity difference may not be present. However, AFAIK improved interrupt handling is a major reason server systems were designed to use server CPUs before it started to become common on desktops since I/O is the most important thing for many server-type loads (though not all).
As a comment to davr -- knowing how a system handles interrupts can be very important when deciding on a hardware purchase, particularily for high-end systems that are expected to handle high rates of I/O transactions.