I don't believe that string through adds any tension. The effective length of the string is between the bridge saddle and the nut no matter how you slice it. Tuning to pitch sets each string to a specific tension regardless how much string is behind the bridge or through the guitar.

There are plenty of hardtail choices that don't require the neck to be angled. You could choose the fairly standard flat mount Fender style bridges (like those used on hardtail Strats). I believe you could find these at quite a few retailers in both a wide, vintage spread and a more narrow, modern string spread. I would recommend you go a step further and look into the Hipshot hardtail bridges. IMO, Hipshot makes spectacular trems and hardtails.
"To crush your enemies, to see them driven before you, and hear the lamentation of their women." - The Governator