The IRS permits such loans, but it is rare to find a plan that allows it. In the vast majority of cases, you cannot.
Though the IRS permits it, the administrative burden of a defined benefit plan is already significant for an employer, and it is much more likely that they will not make a provision for loans in the plan document.
As far as the IRS is concerned, generally speaking, these plans have the same rules as other qualified plans. If a small partnership or LLC with a cash balance plan wants to put loan provisions into their plan document, they can do it.
Where do I Get Started in Saving for Retirement?
How Does a 401(k) Compare With Other Retirement Plans?