My situation: I installed JMS multisite on a VPS running Linux, PHP 5, etc.
My environment uses DirectAdmin as management environment. This environment
only allows you to direct subdomains to their own homedirectory. So f.i.
subdomain.domain.com points to ../public_html/subdomain

This is not something you can change easily in the DirectAdmin enviroment.
The only thing you must not forget after creating the subdomains (and thus
automatically the respective subdirectories with the same name) is to set
the proper rights to these subdirectories.

My environment supports symbolic links.

Installation of JMS multisite works fine. I am also able to creacte new
sites on the subdomain(s). I also can install new extentions in the master
en 'distribute' them from the master to the subdomains with the Multi Sites
menu in the Master website.

When I install a new template in the master website, the same template is
NOT visible in the subdomains.

As a 'work around' I copied the template directory of the master to the
subdomain, but I am not sure if this is the recommended procedure. Please
give me some advise.

Create a JMS Templates where you specify that you want to share the Joomla template directory.
See tutorial video 0.b slide 34 that show the different cases.
You can get inspired of the tutorial video CP-05 to help you configure the JMS template that will be used to share the Joomla template.
www.jms2win.com/tutorial#jms12x-0b
www.jms2win.com/tutorial#jms12x-CP-05

See also similar question posted in the forum that here want to have a specific directory
www.jms2win.com/forum/23-general-questio...s-directory-question

I had the same problem, but looking at this information did help me.

It seems that you have to use another site as a JMS Template, and put the full path to the templates folder in the deployed site's directory structure as the Theme path. I used Template1 as the JMS template site, and created template1b based on it.

I can see all my templates from the Master in template1b, the deployed site.