They may help you keep the business you have, but just about nothing IT can do will sell one more unit of product, or add one new customer.
Umm, what?!?! Even if IT isn't customer facing, they can still make internal tools and resources to help the salesforce. Sure, IT itself may never make a sale directly, but when the sales person in the field is able to pull up data and information compiled by IT, or use a tool IT created, to help land a customer, then IT most certainly did in fact do something to help sell more product.
Personally, I think the bigger issue is the historical disconnect between IT and Sales. The CEO feels that and it lessens the perceived value of IT. But, when IT and Sales can work together, you can create some extremely powerful sales tools that will absolutely impact revenue. And when you do, the CEO will take notice. But that requires a CIO and IT staff that can work with Sales to help get that done.
At my company, if Sales has an ask, we talk and see how to best do what they're looking for. And if I think of something that might be useful, I'll approach Sales and ask if my idea would be of any use to them. If so, we'll hammer out details and add it to the project list. And because of that willingness to work together, we've created stuff that absolutely drives business. And that flexibility has kept my whole team employed through 4 different buyouts over the past 10 years.
Yes, IT has to keep the servers up and the desktops running and virus free, and that's not glamorous, and doesn't make for spectacular headlines. But IT can go far beyond that, and needs to if it wants a serious place in the business beyond just "janitors." And maybe if the CIO doesn't understand that, then the CEO's derision is justified.