For reasons too long to easily explain, I would like to use dd to image the drive of a physical server and write that drive into a VMware virtual disk. When I use "dd if=/dev/sda1 of=/mnt/networkshare/someimage.img" to image the /dev/sda1 partition into a file on a network share, I'm unable to use losetup to mount it as an image, it doesn't see a filesystem. Shouldn't this be possible? I tried using "dd if=/mnt/networkshare/someimage.img of=/dev/sda1" on a fresh VM to write it back out into the new location, and it can't mount that filesystem. Not sure what I'm doing wrong, dd should be able to image drives this way. Ideally I'd like to just replace the disk and boot into this environment, but even if that doesn't work, I should still be able to mount it as a disk in an existing VM and copy the data over.

filesystem is ext3. DD was run on a mounted filesystem, and I know this is a no-no, but the system is under very little load most of the time and writes are very infrequent. I'll accept some level of file corruption, but I should be able to see the filesystem.

(TL; DR version of why I have to do it this way: VMware converter fails to convert this machine, software is an old version of Debian 5 (Lenny) and the package management is broken. If I can virtualize this, I can start to use snapshots and try to repair the damage and incorporate into our backup system)

You're using dd to clone a partition to a different type of drive.
Why should it? It copies and converts bytes, it has no knowledge of what a filesystem is or how to convert things like partition information, sector offset tables, etc.
In the past I've had some success booting clonezilla to image a drive then creating an empty VM with a suitable empty drive and then using clonezilla to restore. However, if your existng machine has any non-standard drive types, controllers, etc. then you may find that simply restoring an image to a host won't work either.

That might be true if all the meta-data was disk resident. What about all that cache/slab that Linux makes use of. Snaps get around this by use of fsfreeze and CoW.
What does "file" make of that img file ?.