While technically possible to crete a VIF with just one interface, the obvious question is why? You mentioned you are new to NetApp - here's a very generic overview of NetApp VIFs.
A VIF (literally Virtual InterFace, aka interface group or ifgrp) is a logical network port built on top of physical network port(s) or other VIFs. VIFs allow creation of amplified capability - port failover, increased total bandwidth at a single logical endpoint, etc.
VIFs take one of two distinct modes - "single mode" where only one member of the VIF is active, and "multi-mode" where multiple physical ports in the VIF are simultaneously active. Single mode VIFs provide failover between a group of ports. One port and only one is active, the others are "passive". If the active port stops working for any reason, communication can switch to one of the passive ports. The assumption is that the passive ports are configured to allow communication in the same network configuration as was the formerly active port.
Multi-mode VIFs will send data over all member ports at the same time. There are two variations of these as well - a basic multi-mode which is essentially port bonding and an advanced controllable mode using LACP as a control protocol. Which multi-mode option you might be able to use depends on what your switch supports. A basic switch might support simple port-bonding only, whereas higher end switches might be able to distribute the various members of an LACP type mult-mode VIF across physical switches.
Two or more multi-mode VIFs can be members of a higher level single mode VIF. That way you have a single logical endpoint that can flip between groups of physical connections to switches. It can be as complex or as simple as you like.
So back to your question. In your configuration you note port e0a and e0b are running at different speeds. I'm going to guess they are connected to different switches as well, athough they could be to the same switch at different speeds of course.
To your question - yes you can create a single-mode VIF or at least a basic multi-mode VIF and assign it e0b as a single member. If you never associated another port to the VIF, you gain nothing over using it as port e0b directly. Which leads back to "why"? If your intent is to use both ports e0a and e0b for a failover singlemode VIF, that begs the question of the entire network design given they currently run at different speeds.
If you have time to respond it would be helpful to know what you want to accomplish and why you are considering a VIF in this configuration.