** Full Disclosure** I work at IONODES. IONODES does make Secure Display Stations (SDS) which do decode ONVIF streams and work with many different IP cameras. IONODES Secure Display Station (SDS) link
While our decoders are compatible with, and work with ONVIF Profile S; I didn't respond earlier because of the term "compliant decoders." IONODES SDS' (ION-R100S & ION-R200) are not on ONVIF's list of conformant products.
ONVIF considers decoders as "Clients" and lumps them in with DVR's and VMS clients that record and display streams from IP cams. So the Client standard and testing regimen has a bunch of stuff that doesn't apply to decoders. (For example, how to configure IP cams from the client software.)
As a result, very few decoders are listed. In this thread for example: The Aimetis Thin Client A10 decoder is listed but the Hanwha SPD-150 is not. As stated earlier IONODES is not listed either. The Hanwha SPD-150 may be "conformant" and listed under another name. My point is that things are a bit unclear when it comes to ONVIF and therms like "compliance" and "conformance"
ONVIF Conformant Product Search