My google search did not really answer my questions on pre-glued dowels.  It did indicate that it was less messy and quicker to use pre-glued dowels.  It did show that the fluted (straight grooves) performed much better than the helical groove dowels (in pre-glue).

But it did not show the relative strengths of the pre-glued vs. site-applied glue dowels.  It may be a non-question.  Perhaps both are strong enough.

https://www.google.com/search?q=pre-glued+vs+non+glued+dowels&client=firefox-b-1-d&ei=zVMdYMnLFMWo5gKZ_4D4Cw&start=20&sa=N&ved=2ahUKEwiJ5t__99LuAhVFlFkKHZk_AL84ChDy0wN6BAgIEDg&biw=1384&bih=786

Anyone have experience using pre-glued dowels?

From what was available online it seems that the pre-glued dowels have found these advantages of pre-glued:

1.  Faster
2.  No squeeze-out that might affect finishing
3.  less labor = less expense (not a factor for hobby-builders)

Pre-glued requires a properly fitted dowel/hole.  Pre-glued will not fill voids left from oversized holes.

While the instructions vary, most call for filling the hole 1/3 full with water.  The dowel pin then forces the water up through the entire length of the hole.  The water softens the glue and allows the dowel to absorb the water causing it to expand for a tighter fit.

The glue is " uncatalyzed, water-activated, PVA (Polyvinyl Acetate) glue".  Once the glue is dissolved I would assume it makes contact with the mating surfaces.

For cabinets pull-out strength of the pins seems less of an issue than shear and racking forces. 

I am not defending the pre-glued dowels.  I am trying to learn if the advantages are offset by some unknown to me disadvantages.

So far I have not found much on the downside.

I didn't even know pre-glued dowels existed.

What I do know is I always use wood glue that can stand water, so I would never use pre-glued dowels.

I have used both with the VS 500 (which dates me). I initially used pre-glued dowels and was glad when I used them  all up. I switched to plain fluted dowels and am much happier. I found wetting the dowels to be a pain in the butt.

A rather interesting idea for production shops. Not so much for the hobbyist. With an automated water dispensing mechanism you could really fine tune the amount of water injected into each hole and maintain the hole-to-hole consistency.

I think the largest issue for the hobbyist is accurately measuring the water doses and filing the dowel holes...I think a syringe with graduations would be a big help. Too much water and the glue gets too diluted, too little water and the glue doesn't soften up and flow like it should.

I also wonder if there are guidelines on assembly times for different wood species as I assume cedar absorbs water at a faster rate than hard maple?

pre-glued would make more sense to me if they used a glue that was set via thermal.  Either you put it together and run a heat gun by it for a moment, or the friction of being pounded together makes enough heat to activate the glue, like coated sinker nails that the heat from the friction activate the glue on the nail.

When I started working with dowels, I thought pre-glued dowels sounded like a good idea. I bought a lot of 6 and 8mm dowels. I tried all the methods you mentioned and found them to to be more complicated than I anticipated. Try them both and see which you prefer. Dry fitting joints with pre-glued dowels is particularly irritating. It is all too easy to transfer some of the glue to the work dry or wet. The water as well I found hard to control no matter how carefully I prepared.