I am in a condominium with a single boiler and all of the units split the cost of heat. Is it possible to add individual meters for each apartment? The heat is by hot water baseboards so, I'm assuming there are zone valves. I was not able to find a system to monitor usage by zone valve.

Nope, if there is only one boiler, then one gas supply and one electrical supply is run to it, there is no way to equally split the cost to other tenants,, only way would be to have each individual unit have their own gas meter, electric meter, and separate heating system.