Before starting the project, I spoke with FIRST marketing, and they confirmed that the use of the logo on a not-for-profit product such as this is consistent with the "Policy on the Use of FIRST Trademarks and Copyrighted Materials (including FIRST and The LEGO Group Intellectual Property)" and its compliment, the "FIRST Branding & Design Standards."
Of particular interest is the following clause of the Branding & Design standards, on page 7:
"The FIRST® wordmark and interlocking triangle, circle, and square
graphic icon element may be used as separate branding pieces but
MUST not be the only representation of the logo. Either the Vertical or
Horizontal MUST appear in its original designed configuration some
where in the materials."
This is the clause that permits me to use the logo without the wordmark attached on the back of the deck, provided I include the complete logo somewhere in the materials (right now, I plan to put it on the face of each card). You'll note that, as the card faces are not shown on the project image, I placed the complete logo in the corner of the image.