Clusters return in Gat Out of Hell, with the same function, although you now have the ability to fly, meaning most of them will require you to do so. There are two kinds of Soul Clusters in the game, with the first one being blue ones that sit in place and are worth one Cluster. The other kind, which are pink/purple in color, will split into four smaller ones when you touch it.
It may seem random, but the second kind will split in a specific pattern, which you can tell by the arrow that comes off of it. Collect the four parts before they disappear and you will get five clusters. To make things easier when collecting Soul Clusters, wait until you hit level 15 and purchase the Collectible Finder upgrade, which will put all of them on the map.