Is it good design for an unmanaged ethernet switch to be part of a redundant ring?
No. Unmanaged switches do not recognise redundancy protocols like HiPER-Ring or RSTP. In a ring fail-over scenario for example, when the ring manager issues a 'flush address table ' command, this is not acted upon by the unmanaged switch, leading to delays in effecting a full changeover for all data paths.
The Hirschmann RSB entry-level range of managed switches can be a good choice for applications where a more economical switch is required. RSB supports all HiPER-Ring functions except for acting as a Ring Manager.