Can a large block of units move right through a single allied tray? I.e. I have a 3x4 block of renamimates, and a lone carrion lancer out in front. Can they simply walk right through it so long as it doesn't overlap at the end?

59.3 -- If the unit would overlap no more than a single tray of an allied unit during a move and does not overlap any part of that allied unit at the end of the move, that allied unit is not treated as an obstacle and does not cause a collision.

Yep, you can run through any allied single tray. You can even go through a larger unit as long as you only move through one tray of that unit.

What if that CL is on a 45 degree angle or so, engaged with an enemy unit. Now you charge forward with a second unit, which can 'skip' over the single-tray CL and collide with the enemy. Does the 'end of the move' wording above apply to after the squaring up? or do you need a clean spot to land on for the initial collision?

Tactically I'm wondering if you can use a single tray CL out front of your large block of dudes as a redirector against enemy charges. Force them to engage your lone tray outfront, at an oblique angle, so you can counter charge w/ a flank since they had to turn during their squaring up.

Edit: I can simplify the question down to this: When does movement end? After collision, or after squaring up?

Movement must end to determine that you collided, so that happens before you square up. If you cannot end your movement clear of your unit, before squaring up, you can't make the move.