There are several trees to which the name mahogany is applied, and yes, I have seen poorer types used in crating. Sections of my greenhouse were received in mahogany crates.

The mahogany used in 19th c. furniture was often the Caribbean (West Indies), which is now rare. Honduras and other Central American mahogany from related species is less dense. These belong to the genus "Swietenia." 'African' mahogany ("Khaya"), is also a good hardwood; often used for sides and back of stringed instruments (Khaya ivorensis). Orher mahoganies from central and south America also are used. Something called 'Philippine mahogany' from Asian forests is really related to cedar, and several species of Asian hardwoods have been called mahogany but really belong to other genera or families.

There are sites on the internet which discuss woods.
A little here- www.mahoganymall.com. and here- www.the freedictionary.com/mahogany.
Guitars of African mahogany- www.ellisguitars.com/KhayaMahogany.html, a site which discusses other woods used in guitars; rosewood, etc.

It would be doubtful that mahogany used in crating would be of qualities satisfactory for quality stringed instruments.