Hi Sue,
I had a rabies jab before going to Costa Rica - in the somewhat unlikely event I might get bitten by a monkey! I really do not think it is needed, certainly not for the Borneo tour (I did it last year) as you will not be getting that close to the wildlife (you'll probably be wishing you were in fact a bit closer to them!). In any case, the rabies jab allows you 72 hours to get to a medical centre and you could certainly do this with ease on the Borneo tour, not that I'm sure you'd need it!
This is a great tour - especially the three days at the lodges. I hope you are doing Singapore as well, it was the icing on the cake!
All the best,
Bob