Depends on your policy, but the common answer is 'yes'. Same if you have a diamond ring that's stolen; you must have documented proof that the expensive item exists prior to the robbery.
That may depend upon the insurance company. I use USAA, and they do not require that I list the actual firearms. My homeowner's policy includes a specific dollar limit on theft of firearms, but I purchase an extra amount of insurance specifically for firearms which may or may not cover the cost of the actual guns on hand at any one time. I do have a very strong safe, but it is only large enough to contain my handguns. So my long guns could be stolen from where they are stored with less security. I guess my approach is sort of a compromise, but given the restraints of my available space, I feel that's acceptable.
