You can take an image of a virtual machine (VM) when it's running live; the real question lies in the process you have to go through to do so. Normally, any type of traditional imaging technology is going to require that you shut the machine down so it gets every file and every block on the disk.
In a VM, it's really no different. To do a simple copy of the files, you would have to shut the VM down so that the locks on those files would be released. But VMware offers an option that they call snapshotting, which really creates a second disk file that any writes will go to so that you can copy the virtual and configuration disk files without locks. So once you are done copying that image, it will then take the data that was written into that second file and copy that data into the original hard disk file. So, yes, you can take an image of a VM online. You just have to follow a specific procedure to do so.
One thing to also look for is if your backup software vendors support VMware Consolidated Backup (VCB) integration. So we see a lot of Backup Exec, CommVault, Veritas NetBackup and a little bit of TSM in the SMB space. Having that integration really opens the door for more automation and less scripting, which is a key factor for the SMB environment where the business may not have the amount of time or right skills to do that work.