In places where tropical milkweed is native, do monarchs have a high incidence of OE as well?

The short answer is 'sometimes but not always.' The long answer is that monarchs breeding year round on tropical milkweeds in some places like Australia, Hawaii, Bermuda, South Florida do have very high infection rates with OE.  In Hawaii it is very variable - some local sites on some islands have low prevalence and some have nearly 100%.  In Australia it can be variable too. Other locations such as Belize and Costa Rica, where monarchs breed on A. curassavica, are on the lower end of the spectrum with about 20-30% heavy infection rates.  Further research is needed into why this variability exists.