The cost of weapon swapping is around 100 dps, and the difference between dagger-hemo HAT and axe-hemo HAT is around 120, so without playing it myself, my wild guess would be that I would not bother playing with a slow mainhand and then worry about weapon swapping before a shadow dance. I would just stick with a dagger.
have you count with -40dps decrease for poor equipped rogues- around 5000 AP buffed, because the should deadly MH and insta off hand, instead of wound MH and deadly OH?
and other way +40 and more dps increase if you are 8000 AP buffed, co the same thing (i made simple excel sheet, where i used 2,6 weapon for instant/wound , 1,4 for deadly, 20% haste, 13% off hand miss chance, can upload it if need it
plus bigger chance to keep deadly up, and raise it to full 5 stack quicker if it falls down. Ideal in fight like Sindragosa (in Sindragosa fight is shadow step -> priceless