Is otool available in a stock OS X installation with no Xcode? Is /usr/bin/otool available in a stock OS X installation where Xcode hasn’t been installed?
No, it's part of the CLI Developer Tools package in the XCode download:

andy:/Volumes/Xcode and iOS SDK/Packages$ pkgutil  --payload-files DeveloperToolsCLI.pkg |grep otool
./usr/bin/otool
./usr/share/man/man1/otool.1