Does LVM need a partition table?

Even if LVM itself doesn't care about having a real partition, one reason to create it anyway is to inform partitioning programs that there's "something there." A nightmare scenario is a new sysadmin diagnosing a boot problem on a server, firing up a partitioning program, seeing unpartitioned disks, and concluding that the drive is corrupt.

I see no downside to creating an LVM partition. Do you?

While you can just create a pv out of raw block device I normally try to avoid it as it can cause confusion as to what the block device is being used for. It may also break some of the auto discover routines that LVM can use if it's missing it's configuration files.

Here's an example of using parted to create a GPT with 1 partition that is the whole drive and set the partition flag to be lvm. The mkpart requires that you specify a file system but it doesn't create the file system. Seems to be a long standing bug in parted. Also the start offset of 1M is to ensure that you get proper alignment.

parted /dev/sdb
mklabel GPT
mkpart primary ext2 1M 100%
set 1 lvm on

If you create a PV directly on a virtual storage device inside a KVM guest, then you will notice that the logical volumes from the guest are visible on the hypervisor. This can make things quite confusing if you use the same logical volume and volume group names across multiple guests. You may also get some warnings on the hypervisor saying that it can't find a device.

For example, I have recreated this problem on my test hypervisor:

[root@testhost ~]# vgs
  Couldn't find device with uuid dCaylp-1kvL-syiF-A2bW-NTPP-Ehlb-gtfxZz.
  VG          #PV #LV #SN Attr   VSize   VFree  
  vg_main       2   2   0 wz-pn-  19.25g 768.00m
  vg_main       2   2   0 wz-pn-  19.25g 768.00m
  vg_testhost   1   8   0 wz--n- 237.98g 120.15g

Here you can see 2 volume groups with the same name, both from guests which shouldn't really appear on the hypervisor.

For this reason, I would advise that you use parted or fdisk to create a KVM partition on there first (as shown in the previous answer by 3dinfluence), before creating a PV and adding it to a volume group. That way, the guest logical volumes remain hidden from the hypervisor.