In 4E, teleports require line of sight, but do *not* require line of effect. You could teleport through a glass window, no problem.

So, in general, if a power gives you line of sight where otherwise you would not have it, the answer is "yes, you can teleport there". That is, provided the distance teleported from your location does not exceed normal restrictions. The distance teleported is based on your physical location, not your viewpoint. So you cannot combine the powers to travel further than normal. But you could use the combination to teleport through walls and around corners.

Regarding "Seer's Clairvoyance", it does appear to give you line of sight from a separate location, it is a Close Burst 20 power. This means:

 * The power combination definitely allows you to teleport around corners, or into locations hidden from your physical position. 

 * Close Burst 20 is not affected by line-of-sight issues, just line-of-effect. So that does allow you to get a vision located on the other side of a wall of fog, or to get past an illusionary wall, or if you are engulfed by a darkness effect.

 * I am told (in comments) that Seer's Clairvoyance specifically mentions the ability to get a viewpoint anywhere within 20 squares, ignoring line of effect. If that is true, the combination with Fey Step would allow you see into blocked off areas and teleport through 4 squares of solid rock. So you could bypass quite a few barriers (on your own, not always wise!) This seems a bit powerful for Heroic Tier power combination, but is IMO the correct RAW reading of a power that gave you a new Line of Sight unrestricted by Line of Effect, combined with a teleport.

 * Your teleport range is not extended. You may still only Fey Step for 5 squares as standard.