There really is nothing within the whole star tours structure that precludes going back in time line. Droids have always existed from the earliest SW fiction, space travel, the stars and tours of the stars.
The only block is within the minds of past riders who have locked onto "empire vs rebels" from Ep 6 on.
There are specific characters, C3PO and R2, whose creation story is set in specific time, but they could be changed out - new stars created! - to get past (heh, past) the creation dates.
Still, they existed in the Rogue timeframe.
Besides nobody (99%?) ever bothers to question why the pair are suddenly working the tour circuit instead of in battle against the empire. So keeping them driving the bus all the way back to earliest time, say the first episode of the animated series, wouldn't matter much at all the the riders.