I'm not very experienced with SmartDraw beyond creating Mind-Maps and Gantt charts, but I'll tell you what I've experienced:
I haven't found a way to 'import' Excel files, but I've created Gantt Charts by copying the the Excel data and pasting it straight into the Gantt. I opened the Gantt and added enough tasks (lines) to hold the data and then pasted it.
When working with Gantts, I don't add lines using the Table tab, I use the SmartBar to add tasks, one at a time.
Sorry I can't offer more...
Solon