No. No "plumples" or "applums." This article mentions every other plum hybrid with other fruits but makes no mention of an apple-plum hybrid. If it exist I am almost positive they would have mentioned it.
You have to scroll down a bit but it says this:
" the plumcot (P. domestica x P. armeniaca) is a hybrid between the plum and apricot. Some of these hybrids have many different named cultivars, depending on which varieties of stone fruits have been crossed together. In addition, hybrids often retain more characteristics of one parent and are given special names. For example, some cultivars of plumcots are called "pluots" because these resemble plums more than apricots. Plumcots called "apriums" resemble apricots more than plums.
Plumcots, a delicious hybrid between the plum (Prunus domestica) and apricot (P. armeniaca). Since this cultivar resembles its plum parent more than its apricot parent, it is called a "pluot." Plumcot cultivars that resemble apricots more than plums are called "apriums." End quote.
The plum tree and apple tree are in two different subfamilies. Unlike the plum and apricot which is in the same genus. Some oak trees in the same genus will hybridize, for example.
Can an apple tree pollinate a plum tree and vice versa? Assuming they flower at the same time...?
No. And you need different varieties of the trees to pollinate.
Never spray when apples or plum's bloom.