Mail merges work fine with spreadsheets as the data source. You create a spreadsheet of data, then choose File > New > Database, specify connecting to an existing database, Spreadsheet as the type, then click Next and point to the database itself.
Here are a couple things about formats, though.
Formats don't come through. So if you want your Salary field to have dollar signs, decimals, etc. you need to set the format. Likewise with date or time.
One way to do this is just set the formats when you view them. Press F4 and expand to view the query or table you want. Then just right-click on the column heading and choose Column Format.
You can do the same thing in the database file itself. Open the .odb file, click the Tables or the Queries icon at the left, then double-click on the particular table (the sheet or query).
In the window that appears, right-click on the column heading, choose Column Format as before...
and in the window that appears, as before, make the choice you want. Click OK.
Now, here's a related topic. Can you use the =NOW() function in a spreadsheet and have it interpreted correctly in the database and in mail merges? (Thanks to a Colorado Springs LUG member for this idea.) The answer is Yes.
Here's a spreadsheet with =NOW() showing the absolutely current time and date.
Here's what it looks like, with nothing done to it, in the database view. It needs some tender loving formatting since it's just showing the internal numeric value. Right-click on the column heading and choose Column Format.
Set the format you want. The NOW() function can let you use a date or time format since it contains both.
And now it looks fine in the database view.
When I use this field in a mail merge....
Here's the output when I format the field as a date:
and when I format it as a time.