That's definitely a new pseudobulb. A spike would be much, much thinner, and come from the side of a pbulb, instead of in front of it.
As for whether or not your back bulb would live, I can't say for sure. Personally, I wouldn't risk it. Cutting it off would take food from the new growth, and could possibly lead to that new pbulb being aborted.
My experience with brassias and oncidiums in general is pretty limited but usually the spikes come from between the leaves that come out of the pseudobulbs.
In case no one else has said it, welcome to OB. There's lots to learn and lots of fun learning it.