This is facinating reading to a retired engineer- I can't resist adding my 2-cents.
My salmon boat is a 22' SeaSport (built Bellingham, Wa.) with fully encosed cabin. The windows are heavy duty extru alum clear anodise frames and are tempered glass. No exterior fasteners. They used closed-cell foam gaskets on outside. On the inside, the structural portion of the frames have the glass mounted in heavy black rubber and these frames are screwed every 4" or so.
Previous link was another excellent article by Pascoe. I agree with everything he says! There are times when a "gasket' is exactly what you want- such as window bedding. There are times when a gasket is bad- such as struts. In these cases it is necessary to retorque during the squeeze-out life of the sealant. A gasket here would allow working and degrade the strength of the bolted connection.
Mike, to partially address your concerns (and consistant with what Pascoe says I believe), the last thing you want with windows is to ask them to carry loads from the surrounding structure. If they are doing this, you need to reinforce the boat! Crashing through waves is, of course, another matter. I don't know if tempered or lammy has the edge.
Gary