I can only guess the IDE device was due to a CD/DVD-ROM drive that was present in the physical hardware of the Windows 2003 system that you converted. And now the hardware where the VM runs doesn't have a CD/DVD-ROM drive.
Coming from a VMware Workstation/Fusion world, the VM configuration can be changed/edited so that the IDE device is not powered on during startup. I would assume some similar capability exists in ESXi.
It's true, works fine.
Removing the virtual CD/DVD drive is easy.
You should also look at Device Manager for any hidden devices that are no longer needed nor valid for the VM.
An example of a hidden NIC having side-effect after P2V is detailed in the link below.
In addition to removing hidden devices, software that were present in the physical server may also not be required anymore in the VM. But these software obviously can be customer specific and also specific to the vendor of the server that was converted in P2V to VM. Examples I can think of: Intel PROset software to manage multiple Intel NIC cards/ports, IBM ServerRAID software to manage RAID arrays, or tape backup software.