Yes, preprints are available in Dimensions and are included as one of the publication types (the other publication types are articles, chapters, monographs, edited books and proceedings) available in the "publication type" filter on the left of the Dimensions page (see screenshot).

Many preprints are later published in peer-reviewed journals. Where it is possible, Dimensions includes a link on the preprint page to the peer-reviewed journal article that correlates to it (see below for example), as well as links to the original page and full text document.