I think it would be very useful to let a Service Provider to access the appointment admin panel and deal with his/her appointments.
Actually the FAQ of A+ says:
"Appointment records can only be edited on the admin side appointment page. Use an appropriate role/capability manager plugin and grant "manage_options" capability to your service providers. There are some plugins that let you select particular roles, even particular users/providers for this purpose."
The problem is: giving a service provider the manage_options capability will give him/her many administrative rights on many other areas of WP installation, so this is not an option.