A credit check is not standard for a TIER 1, it must be requested as an optional extra cost unless the position falls into a specific category, e.g. child care workers. (Note the exception on Table 2 for when a credit check is required on a Tier 1).
The DOD Suitability and Fitness Guide states this: Tier 1 Investigation is the minimum investigation required for federal employment and is conducted for Low-Risk, Nonsensitive Positions. It consists of a NAC with the addition of inquiries and searches of employment, education, residence, and criminal history records during the past 5 years. Written inquiries are sent to current and past employers, schools attended, personal references, and local law enforcement agencies.
As you may note, there is no mention of credit checks for a standard Tier 1. As well, per DoDI 5200.46 the issuance standard for a DoD CAC is the standard Tier 1.