You can run a slightly old version of Eclipse on illumos. The download is here.
Later Eclipse (and SWT) versions didn't have Solaris support. Or any unix variant such AIX or HPUX either, or certain hardware platforms, come to that.
The way I found to fix this is to edit the eclipse.ini file to force the use of GTK2, by adding the following 2 lines in the middle
so that the full eclipse.ini looks like:
The reason this is necessary is because we now have GTK3, and if you don't explicitly force GTK2 you end up with both GTK2 and GTK3 loaded and chaos ensues.
The failure with GTK3 is slightly ironic, given that the reason for dropping Solaris support in eclipse was that we were stuck on GTK2.