ian,
If you're asking, 'Can I graft scions of 'Red Delicious' onto my seedlings and grow a tree that produces 'Red Delicious' apples?', the answer is, yes.
However, seedling apples will typically give you a 'standard' tree - and will typically take longer to come into bearing than varieties grafted onto dwarfing or semi-dwarfing rootstocks; and, seedlings will vary with regard to resistance to various diseases or insect pests.

Ed Laivo, who was one of the propagators/horticulturists at Dave Wilson Nursery, had a really good article, years ago, on rootstocks, entitled. "Dwarf Tree? But, it's so BIG!!!" or something like that...
It pointed out, as most of us here know, that there's nothing magical about rootstocks and size control - they don't just stop the tree from growing when it reaches 6-8-10 feet - YOU, ultimately, are responsible for how big or small your tree is - they grow until they die; prune, prune, prune.

One thing Ed pointed out, is that the terms dwarf, semi-dwarf, standard, don't mean much to most folks - or if they do, they don't fully grasp the concept. For example, if the 'semi-dwarf' tag says, " tree will be 12-18 ft", how many folks realize, that that's potentially as tall as a 2-story home? Or, that the apple on 'standard' rootstock should come with a tag reading "May become as large as an apartment complex, please purchase additional property."

Apples don't come true from seed. The trees that grow from your red delicious seeds are going to be "wild apples", basically likely to be something like a cross between a red delicious and a crabapple, or maybe just a crabapple. Grafting one onto the other won't make any difference. On the other hand, there is a very small but still real chance that your offspring might be the next new wonder apple. For example, the original McIntosh apple was a wild apple seedling found in 1811 on a farm in Upper Canada (now Ontario).

The OP already stated that they are aware they dont come true from seed. They are asking if he can graft a scion from a red delicious on his seedling, and the answer is : the odds are yes you can. There is always a slight chance with incompatibility issues when grafting fruit but as far as I know apples arent known for it..

I will say you do never know what you get. I was suprised by the hardiness of my macintosh seedling!

As I read the OP's question he hopes to produce a red delicious apple tree by grafting two red delicious seedlings, one to the other, neither of which would produce red delicious on its own. So I think he might be thinking that he can gain the advantages of sexual reproduction through grafting. Short answer is "No".

The scion that he grafts from one seedling will be genetically identical to that seedling, and so will all cuttings from it (ignoring sports).

I think you misunderstand this... When you graft you are not mixing DNA, the part you grafted on will grow from there with 100% of the DNA of the grafted piece, and 0% of the root DNA into the upper portion of the tree.

Let these grow but look for something better then red delicious to graft onto it. (red del sucks compared to most others) If you are grafting onto the branches you can get several different apple types onto one tree. Stick around this forum and learn more.