I see on Wikipedia that both Vietnam and Philippines honor an IDP. However I cannot find specific information on whether my motorcycle license would translate and allow me to rent and drive motorcycles in the two countries. Will an IDP allow me to do so?
The IDP is only valid if you carry it along with your normal license; and there are no restrictions on the license type (in other words, if your normal license is endorsed for bikes, then the IDP will also carry that information).
The IDP just acts as a global version of whatever your local license says (its just a translation).
Save for some commercial restrictions - for example, driving of large commercial vehicles, or transporting goods and people commercially - where you need an extra permit; the IDP suffices for all types of land vehicles.
It does not however, exempt you from local laws; for example if you are allowed to drive at 16 in your local domicile, but the legal age for driving is 21 where you are visiting - the IDP will not grant you an exemption.
It also means that if your license has a specific type restriction (I know some licenses are rated for specific class of vehicles) then the same will be written on the IDP and will apply in the foreign country.
I can only speak for the Philippines but any current drivers license will be honored when you have a visitors visa. I've actually been stopped in 3 road blocks in the year 1/2 since I've been here and showing them my US drivers license got me waved through without any further questions.