DSS comes with a complete set of R API.
In many parts of DSS, you can write R code (recipes, notebooks, webapps, …). This R code interacts with DSS (for example, to read datasets) using the R API of DSS.
Most of the R APIs can be used both within DSS and outside of DSS (for example, in RStudio).
The Dataiku R API is contained in several R packages:
dataiku, containing most of the features
dataiku.spark, to work with SparkR in Spark 1.X
dataiku.spark2, to work with SparkR in Spark 2.X
dataiku.sparklyr, to work with sparklyr