There's no need to do split apps, you can apply prodiamine at up to 6 month rate in the spring to cover you for the whole summer. There are limits to how much you can use in a year for both, so you could switch to dithiopyr in the fall for winter weeds.

Will that application still provide as strong of protection as split apps would?

Choose your product, Prodiamine or Dithiopyr. Decide when your weeds germinate. Divide that product to cover the times when the weeds germinate. For me it's a Fall application of Prodiamine August 1 and a Spring app on February 1. That should get me pretty well covered for the weeds I will have issue with based on my weather/ground temps.

Well, with pre-emergent there's no strong or less strong, it either works, or it doesn't. You put down prodiamine at 6 month rate, no seed is going to germinate for 6 months. The stuff is outrageously efficient.

So looking over the labels of the two I notice Lesco Dimension explicitly mentions both spotted and prostrate, but Stonewall only lists prostrate spurge. Is it safe to assume that would also control spotted spurge or should I just be safe and go with Dimension since I have spotted spurge?

I'm not sure, spurge only seems to show up in the areas I can't hit with the spreader but I get both kinds so I use sulfentrazone with a prodiamine chaser. My product of choice is bonide Sedge ender

Here is a link to the university of Purdue showing that a split rate pre-emergent application has better season long control than a single app at full rate. With the best control being Dimension applied in April at .25 pounds per acre, and again early June at another .25 pounds per acre, giving a 97% control in august vs a 76% control when doing a single app at .5 pounds per acre. https://turf.purdue.edu/report/2011/PDF/15_AGRY_Patton_sequential%20apps.pdf