There is no solo requirement for SEP or MEP Ratings.
This is why CRIs can teach for them.
Not training for a Licence - only for a Rating for which there is no solo
requirement - then, by the letter of Part-FCL, no FI has the privileges to
authorise solo flight (because, in this instance, they would be exercising
their CRI privileges)
If it is believed it is allowed then it relies on an FI being the most
"appropriate" Instructor Certificate. I cannot see an FI(R) being appropriate
for this purpose - so no, it cannot count as one of the 25 supervised solos
required to remove the restriction.