I think that 1 hour may be optimistic. Well away from the mid month Ferragosto madness.
For a mid-day arrival there should be all sorts of options ...
the water taxi you're considering, particularly if you have a large group to spread the cost,
Alilaguna to certain stops, adds up if several of you, slow but you don't benefit from the slowness because the cabin is so far down in the boat the visibility is poor to non-existent
bus to P. Roma and vaporetto or walk, depends on hotel location, but fast, frequent and very cheap (2 companies, know the difference) - and the view from the vaporetto can't be beat whichever line you use
... If you want to use the water taxi you can get it at the desk in the airport and walk the longish moving walkway down to both the Alilaguna boats and the water taxis
... if you want the bus to P.Roma it is immediately outside the arrivals hall door.