Hello,
The canonical way to do it is:
1/ configure 2 VLANs over ge-1/3/8, say, VLAN 100 and VLAN 200
2/ add IP addresses on each end
3/ terminate VLAN 100 L3 subinterface (say, ge-1/3/8.100) in "L3_Aerohive" VRF
4/ terminate VLAN 200 L3 subinterface (say, ge-1/3/8.200) in "L3_Voip" VRF
5/ configure OSPFv2 over ge-1/3/8.100 and ge-1/3/8.200 inside these VRFs.
6/ Redistrubute routes of Your choice (MP-iBGP, static, direct etc) into OSPF with OSPF export policies
6a/ optionally, You'd need to disable DN bit and VPN route tag if Extreme side does not see routes from Kunde 2 MX
7/ redistribute routes received from Kunde 1 over OSPF into MP-iBGP on MX side
If You cannot create 2 VLANs on ge-1/3/8 then it becomes more difficult.
HTH
Thx
Alex