Can the efficiency of the immunoprecipitation (testing the positive and negative controls) be assessed using endpoint PCR instead of qPCR?
Yes, it is possible but quantification ability will be limited. Generally we recommend to use qPCR for data analyse, because this method allows to compare quantitatively your IP samples versus INPUT sample. However if it is not possible to use qPCR, but only end-point PCR, it is better to use semi-quantitative PCR to be able to estimate the quantity of the products.