I think saying that monel is "not reactive with aluminum" is overstating the case. Monel is slightly less reactive via galvanic corrosion with aluminum (potential of 0.56 volts) vs. stainless (potential of 0.64 volts). If the parts being attached are stainless, I don't see a huge benefit for monel. A little sealant of some sort to limit the electrical connection between the stainless and the aluminum is a good idea.

You should get a good idea what kind of rivets are in there when you drill the old ones out.