I think this would need a house rule as while the rules clearly state they will get a saving throw if they are to be teleported somewhere they will be falling or hindering terrain. This makes sense until you start thinking about it a little harder.
Example situation using op's ideas:
There are two warlocks the first uses op's idea and creates a teleportation circle to a pool of acid. The other creates one to an empty and unassuming cave that has no natural way out: it is essentially a stone prison with no way in or out besides the circle.
Does it really make sense for an enemy (let's say a high level orc warrior) to be thrown at the first one and get a saving throw, and have a chance to not get thrown into certain death, while he wouldn't get a saving throw being thrown into the second, which will ensure he dies eventually without a way out? (And even if it doesn't die, because of being something like undead, it's stuck there and dealt with.)
While there are some creatures that would easily get out of this second trap, many humanoids cannot. From the warlock's standpoint, both methods are about the same effectiveness since both of the orcs are now somewhere else and no longer have to be dealt with.
Also from the orc's perspective of how would this work, would it be able to see as it is being thrown through the air where that portal is going and if its not safe he has a chance of not being forced through, but if it is safe its still not somewhere that orc would want to go, so does it make sense for the orc not to get a saving throw in this situation.
I guess my point is that the rule they are using is inconsistent in this case. Either allow a saving throw no matter where the teleportation goes, or don't allow one at all.