Well, if the head tube were pretty long, it might. You could wrap around the top of it, cross over and tension around the dropouts and measure, then slide it down to the bottom of the head tube and repeat. I'm guessing if you could actually measure a difference that you could look across the head tube to the seat tube and see it was out.

Some frame builders I know check everything against a frame table. I know some that don't believe in cold setting the main triangle. The amount of force it takes to cold set those big tubes is pretty large, the tools used include some very long solid steel rods. Here's one example:



More on this pic are https://ninelittletubes.wordpress.co...rtland-oregon/.

So, even if you could measure or see the two tubes misaligned, unless you've got some serious fixtures, there's not much you could do about it. Anything less than a full alignment table would risk damaging the frame

For what it's worth, the UBI class teaches one not to worry about main tube aligment. Proper jigging and brazing sequence/procedure will get you a "straight enough" frame. They have a large Marchetti table, but only use it for students to check their finished product. They stated that when they used it in the past, more students destroyed a perfectly rideable frame trying to dial in that last mm than it was worth.