I'm not exactly sure what you mean by "ground noise," but I'm assuming your referring to common mode noise/interference. How such interference is viewed depends greatly on how the SMPS fits into the overall system (is it isolated, do you have a earth/chassis ground, what are you defining as your reference plane, etc).
With a SMPS, the severity of the introduced common mode noise is highly dependent on the details of how the thing is constructed. In isolated converters, the construction of the transformer is especially critical in determining common mode noise. The proper way to reduce common mode interference is to use faraday screens between the transformer windings, but I have never seen this implemented in small DC-DC modules like yours. Having faraday shields on the transistor heatsinks also helps in high voltage/high power supplies, but that shouldn't apply to small modules like this.
If the SMPS isn't designed for low common mode noise, then suppressing it with external filters may be possible, to some extent. But without knowing the details of your system and your requirements, I can't really say much about your case. Mainly my point is that noise/interference is best dealt with at the source, not with external filters.