Hi,
Thanks for your post. OME currently only supports root account for WS-MAN communication with ESXi servers. We'll let marketing know about the ask and can look into supporting read only account for future releases.
As a work around you can use the mechanism suggested in the thread below:
http://en.community.dell.com/techcenter/systems-management/f/4494/t/19476839.aspx
Regards
Abhijit