There's no difference between the NOI requirements for consumer vs. non-consumer applications. Notification can be verbal or by email (it's a very common practice), BUT if the applicant doesn't provide the requested information, either a denial (for incomplete application) or a NOI must be sent. You can find this here:
At its option, a creditor may inform the applicant orally of the need for additional information. If the application remains incomplete, the creditor shall send a notice in accordance with paragraph (c)(1) of this section (an adverse action notice). [§1002.9(c)(3)]
These might also be helpful:
When an application is incomplete regarding information that the applicant can provide and the creditor lacks sufficient data for a credit decision, the creditor may deny the application giving as the reason for denial that the application is incomplete. The creditor has the option, alternatively, of providing a notice of incompleteness under §1002.9(c). [Commentary to §1002.9(a)(1)#3]
IOW, you can deny the application because it's incomplete. OR you can send an NOI (as described below):
If additional information is needed from an applicant, the creditor shall send a written notice to the applicant specifying the information needed, designating a reasonable period of time for the applicant to provide the information and informing the applicant that failure to provide the information requested will result in no further consideration being given to the application. The creditor shall have no further obligation under this section if the applicant fails to respond within the designated time period. If the applicant supplies the requested information within the designated time period, the creditor shall take action on the application and notify the applicant in accordance with paragraph (a) of this section. [§1002.9(c)(2)]
I always like to say "everyone gets a piece of paper". Either you make them a loan, send them a denial, send them a counter-offer/denial, or send them a notice of incompleteness. The only exceptions are applications that are expressly withdrawn [Commentary to §1002.9 #2] or they are approved and the applicant never comes back [§1002.9(e)].