Flydog is correct. In this case, it appears the attempted loophole is the giving of instruction. However, this only applies to required instruction. If spins are being conducted for the purposes of meeting the initial flight instructor certification, this is the only time that a certificate or rating requires anything remotely aerobatic. If two flight instructors are present, both have had the requisite spin training, and the instruction is no longer required. Loophole closed.
Aside from that, two certificated instructions ought to know better.