Can you elaborate a little on what it is you are asking?
If you mean can you drip melting wax on his prostate externally (perineum) as in wax play, then generally the answer would be yes, but it depends on his tolerance for temperature/pain. The massage candles are designed to melt at a lower temperature but can still be hot to some individuals. Since the perineum is a very sensitive area, I would exercise caution.
If you mean can you use the melted oil as a lubricant to massage his prostate anally as butts suggests, then yes it should be safe. I would again be careful with temperature (don't insert hot wax!) and check the ingredients for any possible allergies or sensitivities.