In a private residential parking lot with designated handicapped parking spaces can those spaces be restricted to residents only even if the guest has a handicapped placard?

Definitely yes. In many cases (such as the building I live in) the residents have to pay a monthly or yearly parking fee to the landlord or owner. Some of them may be designated handicapped parking spaces. A guest has no right to occupy the residents' paid-for parking spots. A private residential parking lot is private property, and the landlord or owner has the right to restrict parking as they see fit. A guest, even with a handicapped placard, runs the risk of having their car towed away if they park in a space reserved for residents.