No; prep.ai.mit.edu and its mirror sites provide GCC binaries for Solaris. As a rule, these binaries are not updated as often as the sources are, so if you want the very latest version of gcc/g++, you may need to grab and install binaries for an older version and use it to bootstrap the latest version from source.
The latest gcc binaries on prep.ai.mit.edu and its mirror sites are for version 2.4.5. There are binaries for both the Sparc and the Intel versions of Solaris available. There are also binaries for ``gzip'', the GNU compression utility, which you'll need for uncompressing the binary distribution.