Is a surface mount ressettable fuse a good choice to put on I/O lines or opto-isolator?
You can't get a fuse of any type that will protect against the 40mA limit of an I/O pin, anything greater is not worth putting on the outputs.
My motto has always been that a semiconductor is a device that protected a fuse. That is it will blow before the fuse blows. If you blow a fuse you normally blow a semiconductor.
The only useful application is where you have a large current capability output and you can afford to limit this to at least a quarter of the output with a fuse - this is especially true of resettable poly fuses which take an age to go (up to three seconds).