On the other hand, if these people bring real usefulness to the table (for example by freeing you from stuff you'd rather not do, like dealing with whiny and confused clients etc), then you should accept them and let them contribute as peers.
The other side of the coin is that the company is growing and clearly someone felt it lacked in some areas. If you're interested in those areas (i.e. you want to step up into management), you have an opportunity to do so.
If you are one of those guys who gets the job done, then you shouldn't be giving a flying f* about the managers/HR, their job is to make things easier for you so that you can focus on your core areas of expertise, if that's not happening, you can and should talk to your founders/owners about your concerns.
Remember, you were there before these guys even came into the picture, and you are responsible for the growth of this company which is now even able to afford new people, and I am sure the company owners do realize that.
that's a very dangerous assumption. The company comes first for them. If you can't or won't fit into their vision then, thanks for everything and good luck.