First, let's remember that the 3-3 invasion is not a balanced joseki. The defender gets a better result from it than the invader does.
Let's first examine the simplest case - just blocking black's last move.
You said that this gets complicated. How?
This is very similar to the typical 3-3 invasion, except white has better shape in the corner now than he did before. Among other things, the sequence below doesn't work for black anymore:
As well, black can no longer kill with when he has the marked descent, like he can with the default shape:
So black's weird hane in question is clearly garbage if all goes normally.
What if black plays differently?
This is almost the exact same as another joseki, except for the unfavorable for white marked exchange:
However, sometimes the diagram above, aside from the marked exchange, is better for white than the more normal way for black to play. This is true when black has a considerable investment in the outside area (hence why white entered the corner in the first place), and this joseki is inconsistent with maintaining that investment.
So now that we've considered the normal ways to play, what else is there?
Well, as you've said, the hane on the other side does look a little dubious white, and I think black will come out better from it.
There are other responses too. What about the simple extension? (Also possible: the one-space extension at 'b'.
Black can't play as below, as this leaves the bad aji of the subsequent cut:
Not that you'd have to play the cut right away, but it's always there haunting black, so it's no good. Instead, the proper move is here:
However, you must keep in mind that this allows white sente to ruin black's outside potential.
Finally, what about pushing along for black like you mention? Well, play that out on a real board and then tell me why black would ever choose that fate as opposed to the normal variation.
So either white can live in the corner just as happily as before, or he can come out and ruin black's area. If black does play the hane underneath, I think he must have considerable outside strength in order to try to kill the white group. Thus, black must play
as below. Anything else would be wrong.However, in most cases, white has many answers to black's move, all of which seem to turn out just fine for him. If you just focus on the simple moves, you can very often find a satisfiable result when your opponent plays a questionable non-joseki move.
is too slack in response to 
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