There's one big issue here, if an employee tells you that your company will be better doing X instead of Y is totally your decision,
it can be right or wrong but that employee will never talk to you about that idea again.
Sure, you can have a lot of discussions with your co-founders, but having a combined vision of the project helps a lot.
In my case, having one of my best friends as a co-founder is the best thing that ever happened to me.
You can have as close a relationship with an employee as you do with a founder.
I think the problem is that people get stuck on labels here-- the idea that only cofounders can have an opinion or will have their opinions listened to is probably pretty accurate in reality, but it doesn't have to be that way.
In fact, one of the most valuable and rarest commodities in a high tech startup is humility. Always hire for humility along with confidence- they aren't contradictions!- and show it yourself.
I think that employees are generally pretty good about letting people know when they are doing the wrong thing... even if they think you're not listening. You don't have to listen very close to tell which way the wind is blowing.
The problem is that too many people are too arrogant to take the direction of the wind seriously, and this can actually be worse with co-founders because their grousing can drown out the employees.