Hi Tobias,
No you do NOT have to use a custom Afaria client to install an Ent. application. The reason I asked in my previous note as I would like you to push this application as an optional app. For optional Ent. applications, you will have to have a custom Afaria client so that you can install it from custom Afaria client's ent. app store.
Since you do not have custom Afaria client, no need to test with optional option. Let me review your provided information and get back to you.
Thanks,
Sejal