As far as I can tell you it works pretty fine on powerlinux, I've made some tests with LTTng on Fedora 17 ppc64 months ago. However, as of RHEL 6.3 and SLES 11.2, there isn't RPM packages for LTTng so you must build from source (straightforward though).
I strongly believe it is a good long-term tool to learn because I've seen a LTTng community pretty active and improving it even further. The toolkit is also ease to use, fast and provides several visualization tools (graphical and command-line).
I am going to post in the blog my experiences with LTTng on powerlinux soon.
Yes, you are right. I did some poking around and looks like that LTTng-modules package (even the earlier 2.0 stable
version) needs Linux kernel version 2.6.38 at the minimum. RHEL 6.x
comes with 2.6.32 version of the linux kernel. So it doesn't look like
it is supported for RHEL 6. I was not able to compile lttng-modules
package on RHEL 6.2 (kernel 2.6.32). Guess we will have to wait for RHEL 7 which I
believe is going to be based on Linux kernel version 3.x.