Can the inverter draw current from the 12v system?

I would expect "VB", when carefully typeset, would be V with a subscript B, and it would follow the general convention in electronics of using V for the voltage of something, with a subscript to say the voltage of what. If used in a manual where they couldn't easily set superscripts and subscripts, it would just come out VB. In general, a VB terminal on an ECU might be a terminal that's kept at battery voltage, such as one to keep the memory alive while the car is turned off (only those terminals are often called just B) or one that passes battery voltage along to something downstream of the ECU.

So you might never be completely sure what some terminal is just from a two-letter mnemonic, but you really need to find it on the accompanying diagram (that text should really be "see page IN-41", not something about seepage). There will be a diagram there that will show you the layout of the circuit, the shapes of the connectors, which way the terminals are numbered, and which terminal is the VB that you want.