They seem to be very similar is Tannhauser set within the world of dust?

No, they do not share a a universe.

There are actually a lot of differences, Tannhäuser takes place in a World where Word War 1 never endet, while Dust takes place in World War 2.

The Amount of Mythology and Magic is also a lot higher in Tannhäuser,while Dust focusses on Technology.

But of course both could be considered "Weird War 2" Games (even though is not technically World War 2 in Tannhäuser), but well, Star Wars and Star Trek are both Space Operas

Ahh thank you. I was quite confused. however are the combat systems similar? Tannhauser sounds very similar to dust tactics.

I really don't think the two are compariable in terms of game mechanics. Tann. is about five man squads fighting in an enclosed space, while DT is all about Platoon to Company size forces in a open on mixed enviorment.

As for how combat and LOS are actually resolved, they both use dice, and that's about the only similairity, I mean they don't even use the same kind of dice.

FFG has the DT rule book and a sample of the first 21 pages of the Tann rule book online in PDF, if you take a look at them I'm sure you get a good idea of how they play.