Wordpress Spreadsheet Functionality Question

I want to use this as a Maintenance program for our customers. Ideally they will log into their user on our Wordpess site, and this spread sheet would be available to each customer. They would enter their equipment and descriptions, set a maintenance interval for each equipment.

we don’t provide such ability out-of-box, but you may customize plugin yourself.
Spreadsheet provides ability to set sheet id when initializing.
This feature gives you ability to create a lot of sheets with different data.
So you should probably set different sheet id for each user (the best way would be to set sheet_id = user_id). To do it you should open file wp-content/plugins/dhtmlxspreadsheet/spreadsheet_common.php and find the follow line:

$cfg .= "sheet: '".($this->get('id') ? $this->get('id') : '1')."',\n\t";

It sets spreadsheet id. You may set user id as sheet id:

$userid = 55; // here should be a code to get current user id in wordpress
$cfg .= "sheet: '".$userid."',\n\t";

Now each user will have his own sheet with his own data.