#NeverTrump considering placing another person in nomination for Vice President against Mike Pence
Is that within the rules?
Entirely. No delegates are bound for the VP vote, and the idea that the Presidential nominee picks a VP that is then rubber-stamped by the convention is purely convention (no pun intended).
If another VP nominee candidate garners enough support under Rule 40 (majorities of 8 delegations), there will be a roll call and everything. Seems unlikely given their failure to force a vote on rules changes, but they'll try regardless. Lord knows who their standard bearer would be, though.
With Trump now guaranteed to be the nominee, I suppose the goal is to express dissatisfaction by making the convention as annoying and divisive as possible.