Use SS# as Reporting TIN if DBA w/EIN Number?

Yes, assuming that the account is owned by a sole proprietor (an individual). Don't confuse "DBA" with "sole proprietorship." The two are not the same. "DBA" stands for "doing business as," and can be used by a legal entity, such as an LLC or corporation, that operates using a fictitious name. The example I always use is "Doctors Associates, Inc., DBA SUBWAY" (the sub shop chain).

Back to your question: A sole proprietor reports business income and expenses as part of his or her individual tax return (Form 1040), using his or her Social Security number. The only reason the individual would have an EIN is to withhold and report payroll taxes for employees. Although it would not be incorrect to report interest to the IRS using the EIN assigned to the individual, the IRS would prefer that you use his/her SSN. It says as much on the IRS's form W-9 on which you asked the individual to provide the number.