Most kernels do not talk to hardware directly unless you are talking about a monolithic kernel. Instead, with a micro-kernel architecture a system will use kernel loadable modules (device drivers). So now we can argue about the distinction between the kernel and a device driver - Does the kernel talk to hardware directly if it must go through a device driver? The reason this question is important for your question is because we have to see if we can in any way categorize the way a kernel talks to hardware as using a shell.
Shell requirement 1 - A text based interface that translates a string or series of strings into some action. I'm not sure this is even a requirement of a shell. A Unix CLI translates text but a shell doesn't have to be a CLI. However lets consider it a requirement anyway. Device drivers most definitely can do this. The category of device drivers known as char or character devices receive text and interpret it. How you would implement the device_write method in a char-based device driver - http://www.tldp.org/LDP/lkmpg/2.4/html/x579.html
If being a text interpreter is the only requirement then yep, there is a shell between the OS and hardware.
Shell requirement 2 - A different address space or process. It could be argued that even in a micro-kernel that the char device drivers become a part of the kernel when loaded. If a shell is a layer that forms a separation or boundary between components then a same address space device driver really only has a boundary that is defined by a method call which isn't much of a boundary at all. Can you have a device driver that interprets text AND is in a different address space than the kernel? Most definitely - while not the norm yet if you look into microdrivers or user-space device drivers you'll find that they do exist.
Shell requirement 3 - Purpose. If a "shell" is just a layer around something that is communicated with via a sequence of text then there are shells around hardware. As the most common type of shell that users have interfaced with is a Unix CLI the description of a shell has often been corrupted to describe a Unix CLI instead of the more generic idea of a shell. So if a shell is just a layer around something, yes you have a shell around hardware. If you want to compare it more to a Unix CLI well then my 1st and 2nd requirements above get us most of they way to being similar to a Unix CLI so whats left?
Handle user input - Your examiner asked about a kernel -> hardware shell so I'd argue that handling user input was not in their requirements list of a shell. However would the user ever submit text to a hardware device driver? Maybe...old modems required a series of AT commands to correctly initialize them.
Limited actions - Another characteristic of a shell that is really a Unix CLI characteristic is the translation of user text into system calls - a Unix CLI is really about providing a way to convert text into syscalls and is the users interface to the kernel. So I'd argue that a device driver is not a shell in the Unix CLI sense because it doesn't exist to convert text into system calls (although some syscalls like sprintf might get used).
TLDR; A device driver is a shell but not a Unix CLI.
