Here is my re-statement of your situation:
You care very deeply about your project. Your Program Manager has recently made a decision to bring on new people. You are concerned that these new people are not necessary, and may be detrimental to the project.
More to the point, you do not understand the reason why your PM feels that more people are necessary at this time.
Since you have a good working relationship with your PM, that is your starting point - ask why the change is a good idea. Do not respond immediately - listen to the response you are given, spend some time thinking about, and THEN make a decision. Your PM could be spot on (example: "I believe that you will need more people in about 8 months, and it takes 6 months to actually get them in place. I figure we have about 2 months of wiggle room if I start the process, now. I do not need to waste your valuable time handling what are essentially HR duties...") or could be making a mistake ("I want a bigger office, so I am growing my empire..."), or could be acting upon orders ("The owner is concerned that if you leave or get hit by abus, we're screwed. We need to have a back-up for you in place, just in case...").
Currently, you do not have enough information. If you get stonewalled by the PM, then go over his or her head.