Can my tenant use the bond to pay the final rent?

NO.

It is illegal for a tenant to request that the bond be used to make a rent payment and the tenant is legally required to pay rent up until they vacate the premise and hand over the keys to the landlord.

The purpose of the bond money is to be kept as insurance for the landlord in case there are damages or cleaning required AFTER the tenant has vacated or if the tenant has vacated with their rent in arrears. 

The bond should not be applied for until after the tenant has vacated, handed over the keys and the landlord has inspected the property.