From the lvconvert manpage:
lvconvert will change a linear logical
volume to a mirror logical volume or
to a snapshot of linear volume and
vice versa.
Emphasis mine.
So yes, it should be possible to convert a snapshot into a linear LV or mirror. If that means you can mirror a snapshot and then use it as a linear lv, that's something you would have to try out.
Apparently, the manpage and me we wrond :P I remembered seeing this stuff in the manpage, but I hadn't actually tried converting a snapshot to a linear LV. Having seen the comment below, I decided to check it out. From what I can see now, it is not possible, what ever the manpage may imply, to convert a snapshot to a linear LV. What is possible using lvconvert is to convert a mirror volume to a linear LV. I think the manpage should be edited a bit here.
If someone does find a way to do this, let me know, but from what I know now, I'd say: not possible. Kinda logical when you think of it, because converting a snapshot LV to a linear LV means something in the line of
dd if=linear of=snapshot
Otoh, you can use a snapshot as a logical volume by itself. As I explained here, LVM is just some device mapper magic. So if you would take an LVM snapshot and then use that for your experiments, the original disk would not be touched, but can still keep functioning normally at the same time.
Best Answer
I have not yet tried the new LVM segment types, but the overview is that they are support for the Linux MD RAID personalities in LVM. That is, they are RAID levels 1, 5, 6 etc. using the MD code with the eventual goal of removing the duplicate functionality of LVM's mirroring and having both MD and LVM use the same code.
This is very new stuff so may not be appropriate for a production setup yet.
For example it is still considered a technology preview in RHEL 6.2:
http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/6/html/6.2_Release_Notes/storage.html