NASA Performance Touring rules stratify tires by performance potential. The RA-1's fall into the "+7" category. The other options in this category have similar performance. So, yes the RA-1 would still be legal, but this would give those who can't get them other options.
Options that would fit the rule, and are available in 15" sizes are the Kumho Victoracer, Nitto NT-01, Yokohama Advan AO48, R-888, and remaining RA-1's. These are available at most major race tire shops, and online.
Not all of these tires are available in a 225/50, so we would allow any profile (ie 45 series tires), so long as the width stays at or under 225mm. This would mean a 225/45/15 Nitto, or a 205/50/15 R-888 would be legal, for example, but not a 235/50/15 RA-1 (or any tire that size).