The man page geom_linux_lvm(4) has a bunch of caveats already: you can't allocate/resize LVM volumes from FreeBSD and it only supports linear stripes. If that is all ok you can probably put your root fs on an LVM volume. However I doubt that the FreeBSD loader understands LVM. It will not be able to load the kernel from it, so a separate boot partition is very likely necessary. Using the FreeBSD installer without manual intervention is also right out. I can imagine that this is a configuration not a lot of people have tried, so I'd expect trouble there as well.
LVM is not a file system and neither is ZFS. LVM is volume manager. NetBSD has LVM as well as DragonFly BSD. I am not sure how well it works on those two operating systems as I have never used it outside of the Linux (adding space to a partitions and one other thing which I don't even remember). ZFS is volume manager and a file system in one. I don't use ZFS grow volume feature but IIRC they were not as good as on the Solaris version. Comparing LVM and ZFS is comparing apples and oranges. Based on the formulation of OP original question he is better off not trying FreeBSD.lvm?? There in FreeBSD is zfs. The best filesystem on the word. Zfs is better solution than linux lvm