I recently saw a question in which someone implied that tunneling could foil MITM even if it were implemented while an MITM was taking place. My understanding of tunneling is that it is only capable of stopping MITM if it connects to the actual network before the attack is attempted, otherwise the VPN would be set up between the target and the hacker. Is this correct, or am I somehow confusing this? As a side question, could anyone tell me if an Evil Twin attack can be successfully implemented against a VPN? Thanks.
Evil twin is an attack against wireless networks, it has nothing to do with VPNs. It may be that you are asking whether an attacker could successfully masquerade as a VPN destination in order to trick the source in to thinking it is valid. The answer to this would be a qualified no. Evil twin attacks work because wireless networks generally provide no way for a connecting host to verify the authenticity of the broadcasting station, in the case of VPNs like IPSEC both sides use a shared secret or key pairs to verify each other's authenticity.
An attacker might be able to spoof an IP address and trick one side into connecting, but without the shared secret or correct key pair a VPN would never be allowed to form.