Can I insert a chart in a table and generate a document?

No. This is a current limitation of Apps Script in that charts inserted in table cells can't be read. As a consequence, these are not copied over in the resulting document merge.

As a workaround, it's recommended to convert charts into images (via screenshot or other methods) and insert them into the table cell as Drawings. The Apps Script behind G Merge Plus can properly read images in table cells if these are inserted as Drawings. Here are related articles regarding working with images in your document template:

• Why aren’t images merged to my generated document?
• Converting Images into Drawings with G Merge Plus