Hi grid96,
According to the USA Map-Chips rules the player can not place a meeple on a covert tile when turning it over. But what about any features on the tile that aren't part of the "place a meeple" action?
I have collected a few questions that came up when playing the map with all major expansions:
Ha ha ha! We have an issue here since the Maps are supposed to be played with no additional rules but the ones of the base game and the Map-Chips if included.
Everyone would be tempted to apply all the rules of the expansions used. So let's see how we can solve this conundrum...
My understanding of the covert tiles is the following:
1) A covert tile placed face down reserves a square for its future placement. The square cannot occupied by any other tile by default.
2) A covert tile turned faceup behaves like a printed tile on the map: you can connect to it, but it behaves like it was already placed in a previous turn: you don't place the covert tile; you just reveal it (or discard it) so that's why you cannot place a meeple on it.
3) If the connection is not possible, the revealed covert tile is discarded and the reserved space can be occupied by another tile placed with the usual rules.
So, the bottomline: covert tiles behave like printed tiles but they are not visible to the players until they are revealed.
With all this in mind, this means that any particular features on covert tiles should be treated as if they were on a printed tile but you cannot count on them until the tile is connected and revealed. Before that moment, the features on the tile do not exist for the game. Again, you don't place the covert tile, you just reveal it as part of the landscape.
If the analogy helps, connecting and revealing a covert tile works like extending a feature on the start tile. The tile is already there and you can connect a tile to features on it but you cannot place a meeple onto that tiles. The revealed covert tile works like a preexisting tile on the landscape but that happens to be available just now.
With this approach, the answers to your questions would be the following:
1. Does the dragon get moved when there is a volcano on the covert tile?
No. That volcano should be ignored if we apply the principles indicated above. You didn't place the tile actually.
When shuffling the tiles, you may be interested in checking that no volcano tiles are used as covert tiles.
2. Does the dragon get moved when there is a dragon icon on the covert tile?
No. That dragon should be ignored. You didn't place the tile actually.
When shuffling the tiles, you may be interested in checking that no dragon tiles become a covert tile.
3. Can the player place a tower floor on a tower foundation on the covert tile if their main placed tile shows a tower foundation?
Yes. The tower foundation would be part of the landscape by the end of phase
1. Placing a tile so you can use it to place a tower floor in phase
2. Placing a meeple.
4. a) Can you place a bridge on the main placed tile to make the covert tile fit?
4. b) Can you place a bridge on the covert tile to make it fit?
4. c) Can you place a bridge on the main placed tile and the covert tile to make it fit?
Yes to the three questions. Bridges allow you to tweak tile placement by adding a dynamic road. If using a bridge makes the connection to the revealed tile valid, it may be used as per the usual rules. This means the tile may be required on the tile just placed (first tile placed) or the revealed covert tile.
5. Can you grow or guide your flock twice if the main placed tile and the covert tile both expand your flock?
No. You can only grow your flock with the tile you placed first. As indicated above, the covert tiles bahaves as if it existed before your placement.
6. Does a tile get placed under the covert tile if it features a hill?
There is no specific need, but you could do so. Unless you use magic portals or the flier, the hill on that tile may become irrelevant during the game.
When shuffling the tiles, you may be interested in checking that no hill tiles become a covert tile.
7. a) Does the circus get moved if the covert tile features a circus space?
No, for the same reason discussed above. The covert tile would behave as if placed earlier in the game. So it would not have any effect at this point.
When shuffling the tiles, you may be interested in checking that no circus tiles become a covert tile.
7. b) Does the circus get moved and scored twice if the main placed tile and the covert tile both feature a circus space?
No. It would be scored once for the tile you just placed. The circus space on the covert tile would be ignored.
8. Can the player place a meeple onto an acrobat space on the covert tile since it is adjacent to the main placed tile?
Yes. The acrobat space would be part of the landscape by the end of phase
1. Placing a tile so you can use it to place an acrobat in phase
2. Placing a meeple.
I'm looking forward to hearing your feedback. 
Hope this helps.