if the ESX servers are part of the same dataCenter and share Storage, the you should be able to use vMotion to move the machine from the ESX to the ESXi evironment.
Obviously ChipSet considerations not withstanding. if there are Chipset issues then do a cold Migrate.
If there is no Shared Storage between the two hosts or they are managed by different vCenters, then you could do a V2V conversion with Converter.
Finally you could just use something like Veeams fast SCP to simply copy the files (VM Powered off) to move the VM files from environment to environment.