How would you phrase this question to them? I don't feel like I am getting any clear answers out of them.
It sounds to me like they've given you a clear answer, you're just unwilling to accept that answer for some reason. I guess because you've been given such a negative view of 401(k) plans that you don't think "no hidden fees" is possible?
In the 6 different 401(k) plans I've had, I think I've only had one with "extra" fees on top of the fund expense-ratios. So at least in my industry, such a thing is not unusual.
One of those 401(k) plans was even from GreatWest, which is one that I don't recall having any extra fees. Not that that means all GreatWest plans a "extra-fee-free", since all their plans can likely vary based on different deals with the employers. In my case, no Vanguard funds were offered in that plan, and the S&P500 index fund had a 0.60 ER, so I presume that's how they made their money. In your case, it's likely that your employer is explicitly paying them a fee.