Bill,
I'd just use whatever locally-adapted seedlings you have available. Ideally, well-established 2-3 yr(or older) seedlings that are exhibiting vigorous growth.
Certain seed strains may be preferred in certain areas. Here in KY, seedlings of "Major" are preferred - but I wouldn't recommend them for use in your location. I know that in the past, seedlings of 'Elliott' were widely-used in the Southeast, but I'm not sure how much investigation has really been done as to what seed-strains are best.

You can graft pecan onto hickory, but we usually do it the other way around - hickory on pecan; problem is, pecan is a more rapidly-growing species and tends to grow faster than the hickory rootstock - so, 10 years down the road, you might have a 10" diameter pecan teetering on top of a 5" hickory understock, heading for failure in a wind event.

Good day, I would like to grow my own pecan rootstock from Ukelinga seeds (nuts) and graft it with Ukelinga scion. How do I prepare my seeds to germinate. Will this method work?
I would lay them in layers in moisturised sawdust for a week or 2 weeks and then in water for a day or two before I plant them in a bed. I will wait until the rootstock is 8 to 10 mm thick and graft them with "tongue and groove" method

Collect your seeds and keep them in your refrigerator crisper until spring and then sow them into the ground or into long tree pots, or, direct sow them into the ground during fall, or, direct sow them into pots and into a heated greenhouse that stays above freezing. You can keep them in ziplock bags in your refrigerator if you choose that method. If the bags develop a lot of condensation dry the nuts for a few days and put them back in until such a time that the condensation doesn't build up too thick. Some condensation is good.

Dax

I would like to know at what temperature must I keep my pecan nuts in soaked saw dust for germenating

Don't allow them to freeze if you're growing them in containers in a greenhouse.

Both light of day and temperature tell the nut it's time to germinate. Good germination temps are 78-80F.

Outdoors your will plant your pecan seeds prior to winter and they will germinate the following spring.

Cull out the weak seedlings and keep only the strong ones for grafting onto.

Dax