Thankfully Discovery Scanners don't need to be deployed to work
I agree, the ADS has to be but not the DSS. The DSS is basically an optional upgrade to the scanner that comes already preinstalled on every ship. The basic difference in addition to doing more than the stock scanner is the increase in distance from 500 to 1,000.
However, if one wants to utilize it while in an srv which has it own scanner the DSS must be set to a trigger the same as the ADS. For example, when doing scanning planet or cival war planet scans. One must be in a srv, the DSS must be triggered when pointing at the data scanner and then one triggers the srv's scanner. Took me two days of trying at Quince before realizing one needs to sets of triggers, one to activate it and one to scan it. In the process, I lost two days of missions, once I learned and made a few million which took longer than I could have done in the bubble. The missions for planet scanning dropped to almost nothing. So, back to the bubble I went.
So, install an ADS and a DSS. Set them both to a secondary trigger on your ship. And if and when you need them, they'll work as designed. Yes, there expensive and take two slots. But the worth is well worth it and cost will be returned 1000 times or more.