Plum Trees
 

Last year we planted a 4 in 1 fruit cocktail tree. Peach nectarine apricot and plum (technically 2 different plums one an italian prune plum and the other Sasnta Rosa. I was looking at buying another plum, one called Bubblegum Plum. It says it does better with cross pollination. Will my 4 in 1 be enough to cross pollinate?

Santa Rosa is listed as a pollinator on most of the plum trees I've seen advertised.