This is a subject that has come up several times, when discussing whether certain species can be used for pollination.

Can an ornamental pear be used to pollinate a fruiting pear?

Can an ornamental cherry tree be used to pollinate a fruiting cherry tree?

Can sour cherry varieties be used to pollinate sweet cherry varieties?

Are they considered members of the same species? Can they be crossbred together to create a new lineage?

To understand the answer to these questions, you first have to understand how chromosomes work.

Let me start out with a classic example in the animal kingdom. Horses and donkeys are two separate species, yet they can produce offspring together (called a mule). But the offspring is sterile, and cannot produce further offspring.

Can an ornamental cherry be used to pollinate a fruiting cherry tree? Well I have found one published source that seems to confirm this:

"Since there is no low-chill germplasm available for sweet cherry, the only other alternative is to go to another species of cherry for this trait. Several species have been used in crosses with sweet cherry with occasional success with Prunus pleiocerasus and Prunus campanulata. In 1957, W.E. Lammerts made a cross between P. pleiocerasus and P. avium 'Black Tartarian'. This hybrid is very low-chilling (<200 CU ) but not self fruitful. The hybrid was repeatedly crossed with sweet cherry and P. campanulata. In the mid 1970s, the Florida program developed several seedlings by using mixed pollen (P. campanulata and 'Stella'). All the hybrids had pink blooms and thus were probably hybrids with P. campanulata. Several of these seedlings were fruitful. Although the size is still small, this germplasm is useful for the development of low-chill sweet cherries."

Temperate Fruit Crops in Warm Climates, edited by Amnon Erez, p216

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Prunus campanulata is the Formosan cherry. The Formosan cherry is more distantly related to the other Japanese cherry blossom varieties, but can still be interbred with them and produce fertile offspring.

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Sweet Cherries (Prunus avium) have a 2n=16 chromosome number, though there do exist a few triploid and tetraploid varieties.

Sour Cherries (Prunus cerasus) have 2n=32

Capulin Cherries (Prunus serrotina) have 2n=32

Cherry blossom trees are 2n=16, with the sterile triploid hybrid cultivars (mostly in the serrulata group) having 24 chromosomes. (sterile means they can only be propagated by cuttings)

Protocols for Micropropagation of Woody Trees and Fruits, edited by S.Mohan Jain, H. Häggman, p403

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Sour cherries can be used to pollinate sweet cherries, for the purpose of producing fruit.