from the help... so I guess not, unless the help is out of date
Constants | ArcGIS for Developers
TextFormatting.NewLine
Inserts a new line, or line break, into the text. Multi-line labels are NOT supported in the ArcGIS API 3.x for JavaScript nor in the ArcGIS Online map viewer.
Example
Returns "T2N R1W"
"T" + $feature.TOWNSHIP + TextFormatting.NewLine + "R" + $feature.RANGE