I wonder if Aptana Studio 3 has less css compiler feature. I used the program with Simpless but I didn't have the Simpless turned on by chance. I edited and saved the less file and a css file was created automatically. I searched google but can't find it has that feature. I even moved the Simpless to other drive but it works.
It seems just a little over a year ago it needed just a few tweaks to support LESS. I have not found anything more official than that discussion posting to verify.
This issue is still open at present, but seems to deal more with some editor features as opposed to actual compiling.
However, simply by your testimony that it is working would seem to answer your question. And if the changes to make it work were in fact as simple as the first post link above indicates, I don't know why it would not have been incorporated within the last year.
For syntax highlighting, see this stackoverflow answer.