It is always good to check the
Aurora C# change logs which are as close to documentation as we can get.
The post on ELINT has the answers:
If the target can be detected by the ELINT modules' built-in EM Sensors, intelligence can be gathered.
So make sure the target is within the effective EM sensor range of the ELINT module, which is probably different from any normal EM sensor you might have installed on the same ship.
For populations, the intelligence is also multiplied by (100 - Population Species Xenophobia) / 100. In other words, it is much harder to gain intelligence when a population has high xenophobia. If the alien language is not translated, all intelligence is reduced by 80%.
For Precursors, like any spoiler race
they will not communicate so you will not have a language translation without SM mode, and more importantly I believe Precursors will have 100 Xenophobia since
they are always hostile, so the intelligence multiplier is zero. Basically, trying to cheese the ELINT game to steal tech from Precursors will not work.
EDIT: And also take note of the below:
If the population is less than 100m, the translation of Population Intelligence to Race Intelligence is modified by Population in millions / 100.
So to compound the above, since the colony is unpopulated you will not gain any racial intelligence leading to technology and other goodies anyways.