Yes I believe you can pull a custom field from customers tab on sales invoice if you are using your own “view template” coding.
I pull vehicle from customer tab to show on my invoices.
I will take a look at my template later to see what the coding is and paste it here.
Ah, yes, @Abhishek. @itmoto is correct when you are coding a custom view template. You did not mention you were doing that, so I thought you were trying to add custom fields to the standard sales invoice. You can do that, of course, but with limitations.