No, but you shouldn't have to boot them differently. The 64-bit Solaris 7 kernel is booted by default if it is installed on an UltraSPARC system. If it isn't installed, the 32-bit kernel is booted instead.
Also, on UltraSPARC systems, kadb and various boot programs are now 64-bit programs that can boot either a 32-bit or 64-bit kernel.
If you have problems booting either system type, see the next section.