Right so the asterisk line card allows you to dial in......I didn't know that but you should have no worries with that connection.
The asterisk features page
https://www.asterisk.org/index.php?menu=features lists E&M so if that is what I am used to you should be able to set up E&M tie lines. Try checking E&M with Digium.
I never recommend using a physical extn as the pilot of a UCD group. Use a virtual and then make it busy using CMD E50 de Stn No de 0 exe
Cmd 410 allows you to set variables applying to the sending of the tones like sender pre pause timing & 5000 allows you to prefix digits. All of these may already be set ok though. If not you may have to find compromise settings that suit both your Asterisk and your voicemail
Cmd 08 de 443 de is more problematical as it is a system wide setting and sets whether the VMS extns use DTMF or MCI. If your voicemail is using MCI you would have to see if it can be changed to use DTMF. If not you would have to decide between the two. In this instance E&M tie lines would be the way to go.
Hope this helps