As always when it comes to backing up stuff, do not fully trust answers from the net (like this one ;-)) and test it yourself before handling valuable data.
Taking a look at http://packages.ubuntu.com/maverick/rsync (and there, specifically, at [rsync_3.0.7-2ubuntu1.dsc]), we see that the maintainer writes
-- Paul Slootman <email@example.com> Mon, 20 Nov 2006 15:43:12 +0100
rsync (2.6.9-1) unstable; urgency=low
* New upstream release.
* (from experimental version 2.6.9~pre3-1)
Applied a mix of the patches from Martin Pitt and David H√§rdeman for
LSBfying init script.
* Upstream now includes the patch for replacing a dir with a symlink when
* Now includes the ACL patch.
So the package itself supports ACLs since 2006.
As for your second question: I don't know about tar, but as long as you only rsync your files somewhere else, you should not be affected by any possible problems with tar. rsync does not use tar during transfers.