Here's the way I would get glue line straight edges on rough sawn boards..... with curved edges. I use a lot of rough sawn oak, had it milled here on the property, air dried and and then build with it after it's acclimated in the shop.
I seldom, if ever, need a board longer than 8 Ft, so a piece of 1/4" hard board AKA Masonite, can be the base of the jig. A 1 X 3 is used to strengthen it and as a mount for the toggle clamps. The short fence on the front I have found is optional. Nothing has moved under the clamps as many times as I have used it .... lots.
You run the factory edge of the jig/hardboard against the fence to insure a straight rip on the other side. You clamp the board any manner you need to give the most yield to your piece. Keep pressure in and forward and you will have nice straight edged boards:
I needed to straight line many, actually dozens of pieces, so I made a "jig" rather than scab on strips each time, which is way too time consuming for me.... "snap on" then rip and "snap off'"...next piece...
I made two sizes,one long enough for 8 footers and a 54" for shorter boards. I used 1/4" hardboard for the bottom and a 1 X 3" piece of Oak for the toggles to mount on. It looks like this:
Having said all that, whether you use additional alignment devices or methods like dowels, bisquits or splines MAY depend on your glue up methods and clamps. Proper clamping procedure requires a flat surface to work on, lower and upper clamps tro equalize the pressure and possibly cauls on either end to insure the boards don't slide up or down as the clamp pressure is applied.
I have used bisquits
with good success. I don't use the biscuit joiner as instructed by the manual. I lay the work flat on the table an use the large base of the joiner as my reference, rather than the smaller fence supplied. To get different heights off the table I use a 1/8" or 1/4" plywood as a stick on base to raise the cutter.
I don't like dowels because of the alignment issues not only for height, but laterally.
I have used full length splines on long runs, made the groove with a slot cutter in my router. I use a 1/8" cutter and 1/8" hardboard for the splines. Where the hardboard will show, I stop the groove short, and use a shorter spline.
Sometimes, there are several right/correct answers to the same issue. It depends on skill level, available tools, budget, who it's for, who's paying for it, OR is it a "teaching/learning" experience as this Thread is supposed to be....?
If you don't learn something from every project you make, you have either made many of the them before exactly the same or your methods have become so familiar that it's just a chore and a bore. If that's the case, it may be time to think about making new and better jigs to make repetitive operations more efficient.