Can the generic teleport Action available to some monsters be used to move through transparent, total cover?

Question

Many monsters have access to the Action, teleport.

MM, various statblocks

Teleport. The [creature] magically teleports, along with any equipment it is wearing or carrying, up to [distance] to an unoccupied space it can see.

It is known that spells that grant a teleportation effect target a point that the caster can see. Because a point is targeted, the caster would need not only sight of the destination, but also clear a line of effect per the spell rules in the PHB on casting spells.

PHB p. 204

A Clear Path to the Target

To target something, you must have a clear path to it, so it can’t be behind total cover.

Are monsters that teleport using the above quoted Action required to have a clear line of effect to their destination?

Answer 1

Yes, the creature can teleport to a visible place behind full cover

One thing to be clear about is that this monster ability is not a spell. If it was a spell it would say that the monster "casts [insert spell here]", but it doesn't. Therefore this is simply a magical monster ability.

This is important because the Clear Path to the Target rules only apply to spells. They are in the Casting a Spell section of the rules under the subheading Targets. There is no indication that this rule is meant to apply to non-spell abilities.

Since the monster rule is a completely-packaged monster ability it would state if there were any restrictions such as being able to not work under full cover. Since it does not say anything of the sort, it works according to the rules.

Many teleportation spells work the same way

And even if the rule did apply to monster abilities, there is no indication that it would break that rule. The ability seems to be modeled after the misty step spell (but to be clear is still not considered to be that spell) which only targets the caster of the spell and not the destination.¹ It would seem that the monster ability works the same way, or at least that it is a very very reasonable ruling to make.

Either way, teleporting to a location under full cover that the monster can see is not an issue.

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^{1 - In fact many teleportation spells are like this. So when you say "It is known that spells that grant a teleportation effect target a point that the caster can see." in your question that is actually not true.}

Answer 2

Probably yes.

The monster ability uses almost exactly the same language as misty step.

... you teleport up to 30 feet to an unoccupied space that you can see.

Misty step doesn't target the destination, so you can choose a point behind transparent cover.. The monster ability doesn't say whether it targets anything, but it sure looks like it's intended to work like the spell.

Note: "It is known that spells that grant a teleportation effect target a point that the caster can see." This is generally not true. Misty step and teleport target only the people / objects to be transported. Dimension door might be different, as it has you choose a destination within the spell's range, but it also specifies that you can choose a point you can't see.