It's one and the same form. The form my wife filled out is the same for both Isle of Man and UK. The UK embassy in Manila acts for the Isle of Man too. (There is no such thing as an IOM embassy.) Immigration regs are not exactly the same as for the UK but they are often very close. Things change a bit for ILR etc but the Spouse visa application process is the same.
Having said that, being on the Isle of Man, it is possible to phone the IOM Immigration authorities with ease. Something not possible with the UK embassy in Manila. I did that a couple of times and they were quite helpful. I haven't tried it yet but I get the impression it is possible to almost call round and have a cup of tea with them.
http://www.gov.im/cso/immigration/welcome.xml