If you mean using overloaded functions as they are used in languages like C++, the answer is no. You can simulate this by writing functions that perform the same task, but having different names along with it's parameters. Then give them the same name in the stringtable, but each referencing a different DLL function call and parameter set.
Look at this stringtable from the DBProImageDebug.dll
1,LOAD IMAGE%SL%?LoadEx@@YAXPADH@Z%Filename, Image Number
2,SAVE IMAGE%SL%?SaveEx@@YAXPADH@Z%Filename, Image Number
3,GET IMAGE%LLLLL%?GrabImageEx@@YAXHHHHH@Z%Image Number, Left, Top, Right, Bottom
4,PASTE IMAGE%LLL%?PasteEx@@YAXHHH@Z%Image Number, X, Y
5,DELETE IMAGE%L%?DeleteEx@@YAXH@Z%Image Number
6,IMAGE EXIST[%LL%?GetExistEx@@YAHH@Z%Image Number
7,SET IMAGE COLORKEY%LLL%?SetColorKey@@YAXHHH@Z%Red Value, Green Value, Blue Value
8,PASTE IMAGE%LLLL%?PasteEx@@YAXHHHH@Z%Image Number, X, Y, Transparency
9,ROTATE IMAGE%LL%?RotateImageEx@@YAXHH@Z%Image Number, Angle
10,LOAD IMAGE%SLL%?LoadEx@@YAXPADHH@Z%Filename, Image Number, Texture Flag
11,GET IMAGE%LLLLLL%?GrabImageEx@@YAXHHHHHH@Z%Image Number, Left, Top, Right, Bottom, Texture Flag
12,SAVE ICON FROM IMAGE%SL%?SaveIconFromImage@@YAXPADH@Z%Icon Filename, Image Number
13,DELETE ICON%D%?FreeIcon@@YAXK@Z%Icon Handle
14,LOAD ICON[%DS%?LoadIconA@@YAKPAD@Z%Icon Filename
15,SAVE IMAGE%SLL%?SaveEx@@YAXPADHH@Z%Filename, Image Number, Compression Mode
16,IMAGE WIDTH[%LL%?GetWidth@@YAHH@Z%Image Number
17,IMAGE HEIGHT[%LL%?GetHeight@@YAHH@Z%Image Number
18,LOAD IMAGE%SLLL%?LoadEx@@YAXPADHHH@Z%Filename, Image Number, Texture Flag, Divide Texture Size
19,OPEN IMAGEBLOCK%SL%?OpenImageBlock@@YAXPADH@Z%Filename, Mode
20,CLOSE IMAGEBLOCK%0%?CloseImageBlock@@YAXXZ
21,PERFORM CHECKLIST FOR IMAGEBLOCK FILES%0%?PerformChecklistForImageBlockFiles@@YAXXZ
22,IMAGE FILE EXIST[%LS%?GetImageFileExist@@YAHPAD@Z%Filename
23,EXCLUDE FROM IMAGEBLOCK%S%?ExcludeFromImageBlock@@YAXPAD@Z%Exclude Path
Observe the Image LOAD/SAVE commands. Each version calls a different function with a different number of parameters.
If you mean initializing a parameter with a value if nothing is passed during the function call, that would be no also. The stringtable tells the DBPro compiler what parameters to expect to see passed to the function in the DLL. If not present in the DBPro code, the compiler will complain.