The RT ladder is still probably vulnerable even if the alts aren't actively competing at the same time, since one of them could theoretically inflate the ratings of the other's opponents/etc.
To better explain this:
Person A loses to Person B on purpose multiple times over the course of a week.
Person C beats Person B over and over again.
Person A and Person C are the same person.
In theory, the rating sort of "transfers" over from the main account to a medium, and then onto the alternative account afterwards from there on out or vice versa.
But also in theory, nobody really cares so.