OK, I'll bite.
I disagree with your lending department's interpretation, because I don't think the definition of 'escrow' hinges on whether reserves are collected.
Take a second look at the RESPA definition - it talks about charges that both parties voluntarily agree that the servicer should collect & pay. That's what you're doing with the PMI premium.
I checked the definition of discretionary payments at 3500.17(o), but it doesn't fit because PMI is a settlement service (3500.2(b)(10)) and because it's required by the lender. (This last part assumes you wouldn't make the loan without PMI...)
In our shop, we take 2 months PMI reserve as a cushion at closing. Monthly premiums are listed in the initial & annual analysis, just like 'deposited' amounts from the customer payments and regular disbursements to other insurance companies or taxing authorities.
Hope this is helpful.
_________________________
Opinions are Bartman's, not those of my employer. "A noble spirit embiggens the smallest man."