Generally, the impact fee is not something that the consumer directly pays for. Rather, the developer of the new community/housing is charged an impact fee to help cover the costs associated with adding the infrastructure necessary to support population growth.
A developer may only pass on an impact fee if that line item is specifically identified in the contract that you signed when you put escrow money down on the home. If that item is not defined, you tell the developer that you will not pay it.
Now, if the impact fee was buried in the price of the home, then, yes, you may finance that fee as the fee makes up part of the value of the home. If the impact fee was left as a basic line item, some banks will not let you directly finance that fee.
IF you are a developer, then yes, your commercial lender should allow you to finance a portion (but not likely all) of that fee.