Not strictly.
Think of packer like more of a task sequence. It uses "builders" to handle all target specific work (spinup an AWS EC2 or Azure VM) then runs through the "provisioners" universally across them. They aren't identical in the traditional sense where you expect a byte for byte copy, instead it runs identical tasks across the unique instances to end up wit ha common configuration.
Most people work from marketplace images, which pretty much always include agents specific to the cloud provider, so the resulting images are typically _not_ identical. You could use a Vmware builder and a QEMU builder, point both at an ISO file and run the same steps and end up with something "pretty much identical" ... but it's _not_ doing some mystical "build one server then convert and copy it to multiple targets" trick ... partially because AWS has made that ridiculously difficult.