There are two tags for Emacs viper mode.
As per Emacs Wiki both mean the same thing.
Viper-mode or just Viper is an Emacs mode that emulates vi key bindings.
Shouldn't they be merged?
There is a question Dynamic Memory Allocation Failure Recovery that has viper tag but given the context it refers to the processor. All other questions tagged viper are about Emacs viper-mode.