To answer your question, yes it should be possible to use both dynamic and static IP interface configurations. You do this by creating virtual interfaces to use the same physical interface. Each virtual interface will need to be configured properly to your network's needs.
I am not as familiar with PPPoE but I have found some links that could help you. This post covers how to configure having both static and dynamic interfaces. Here is the Official Debian Wiki on how to set up PPPoE. Again I suggest you read through the Debian Wiki on how to do network configuration using different interface settings.
According to the aforementioned links, your
/etc/network/interfaces should look something like this:
auto lo eth0 eth0:0
iface lo inet loopback
iface eth0 inet dhcp
iface eth0:0 inet manual
iface dsl-provider inet ppp
pre-up /sbin/ifconfig eth0:0 up
Don't forget to run pppoeconf to generate and/or modify /etc/ppp/peers/dsl-provider, /etc/ppp/*ap-secrets files and /etc/network/interfaces.
It is best, in most cases, to keep the suggested answers
I would substitute
eth0 with whatever the name of your device actually appears by default to keep things simple. However I highly suggest you read through the Debian manual on how to set up networking before you do anything. Remember to figure out where your network is getting its configuration information from and make the appropriate changes there. Best of Luck!