This is a leaf spring. A leaf is one individual piece of flat spring steel within the spring pack.
So I should have looked at the fact that your bus has a 6.2L making it smaller and most likely having independent suspension with coil spring. In light of this information, yes, veggie oil could theoretically throw your alignment off, but you're going to need a ton of it to make a small difference. I wouldn't worry about it. I've had to do some alignments on class C (van-based) motorhomes before and I can assure you they are a pain in the ass and when all is said and done they still handle like a motorhome. Other than major toe issues, none of the other alignment issues are going to result in tire wear issues before dry rot sets in for the majority of RV owners.