If you use a high quality Motorcycle Specific Oil such as AMSOIL 10W-40 Motorcycle oil, it already has high levels of ZDDP as the EPA regulations on other oils have not impacted this product.
I would be concerned about low levels of ZDDP in products such as Rotella T series which has API Ratings that, among other things, force lower ZDDP levels to protect DPF systems and it can also affect cat converters as you noted. Interestingly, while there are those that put this oil in their bike simply because it has a JASO rating, it was never intended for motorcycle use. This is a heavy equipment product... see brochure:
http://s08.static-shell.com/content/dam/shell-new/local/business/rotella/downloads/pdf/rotella-triple-brochure.pdf
My 2¢ - we do enough to reduce our environmental footprint by simply riding something with 40 or 50 mpg... no need to force additional emissions regs related to cat converters on motorcycles.
Whatever oil you use - I would stay away from oil additives. They were not considered when the oil was formulated or when the engine was built. Get an oil that has everything you need in it from the beginning...
The only companies you will see recommending oil additives are the additives makers. I've never seen an oil company or machine manufacturer recommend an oil additive to be put in the engine. There is numerous documentation of the false claims of these types of companies including a long list charged by the Federal Trade Commission - most recently ZMax (which you may have seen advertised for a while on gear head type television shows) - FTC nailed them to the wall for deceptive advertising etc...
...Don't waste your money - IMHO
