OwnerDraw means the developer can draw anything - including text. There is NO rule that says text may not be used.
I would expect that in OwnerDraw style (and assigned OnDrawItem) there will be empty area where developer can draw anything; colourful background + some custom text in this case.
I did a test, style OwnerDrawFixed and OwnerDrawVariable:
Wine Laz. 1.2.6:
OnDrawItem assigned: no text
OnDrawItem not assigned: text is there
Qt Laz. 1.3:
OnDrawItem assigned: no text
OnDrawItem not assigned: text is there
GTk2 Laz. 1.3:
OnDrawItem assigned: no text
OnDrawItem not assigned: no text
So the only bug is incosistency in GTk2, it doesn't display text when OnDrawItem is not assigned while other widgetsets do.