The Dropout.tv shows are available to add on trakt, but the Dropout streaming service isn't an option in the filters/favorites tabs.
We get all of our streaming info from JustWatch. I checked their site and it doesn't look like Dropout.tv is one of their options, which is why you can't filter or add it to your favorites on Trakt. I found this link where you can request that JustWatch add a streaming service. I would suggest starting there. If it gets added to JustWatch then it will reflect appropriately on Trakt.