Does adding vegetables to your brine add any flavour?

I've been a fan of brining for a while and NO, adding flavouring to the brine won't make much if any difference in relation to the brining itself, which makes a lot of difference.

I have employed my most wishful thinking many times with brine, on the basis of the fact that pretty much every reference to it in recipes, on cooking shows, etc., always seems to promote the idea that the flavour will diffuse in the brine and be absorbed by the meat. This is some kind of "look at the Emperor's New Clothes" tradition.¹ I've gone to ridiculous extremes to test this, sometimes adding many ounces of e.g., paprika or thyme to < 1 gallon of very salty (4 tbls/quart) brine with a chicken overnight -- which is actually too much time, a few hours is plenty with that much salt. In some cases I've gone overboard with the salty part, but despite all the piles of herbs, powders, an entire bottle of hot sauce, etc., you at best get maybe a hint of something on the surface.

In short, my opinion now is that while brining is awesome for pork and poultry -- salty and moist meat being far superior to dry and bland meat -- adding something to the brine and expecting it makes a difference is a complete waste of time and materials.

As per one of my comments on the question, I'd guess the issue here is that brining exploits osmosis. From wikipedia:

Brining makes cooked meat moister by hydrating the cells of its muscle tissue before cooking, via the process of osmosis, and by allowing the cells to hold on to the water while they are cooked, via the process of denaturation. The brine surrounding the cells has a higher concentration of salt than the fluid within the cells, but the cell fluid has a higher concentration of other solutes. This leads salt ions to diffuse into the cell, whilst the solutes in the cells cannot diffuse through the cell membranes into the brine. The increased salinity of the cell fluid causes the cell to absorb water from the brine via osmosis. The salt introduced into the cell also denatures its proteins. The proteins coagulate, forming a matrix that traps water molecules and holds them during cooking. This prevents the meat from dehydrating.

So the idea is that the meat absorbs salt ions, which then causes it to absorb more water. This is through the cell walls, and I do not think large particles such as the stuff we might associate with "flavour" would be included. Of course, some of the brine may be drawn into the meat between the (large congregations) of cells, but this is probably not a significant volume.

^{1. Some of these recipes call for really paltry amounts of flavoring too, an inadvertent testament to how nice the Emperor must look naked ("Umm -- I can so taste the rosemary from the brine!". Hogwash.). They also often involve paltry amounts of time ("brine for 20 minutes"), I suppose because if you can pretend to taste rosemary you can also pretend to taste salt and appreciate moistness. If you don't have at least an hour, do not bother. At least quadruple that for a whole turkey.}

Adding aromatics to a brine like garlic and onions, and to some extent spices like Bayand coriander, will absolutely impart these flavours in the final product. This is particularly true when brining fish and meats.

While the aromatics and spices will not improve the juiciness, it will impart flavor. If you don't believe me, just add some chopped garlic to your next brine.