Thanks for your information. Development is done in VMs on this server and the upgrade to ESX 5.1 is not planned.
Additional information (another try) :
The USB disk (3 TB disk connected through Asmedia USB3 controler) was not partitionned.
It has been partitionned and connected succesfully to another ESX server having same version (5.0 update 1 releasebuild 623860). On this server, the USB disk attachment to a Linux VM, done in vSphere client, runs successfully and partition can be mounted in the VM.
Will try again on the first server.