There's definitely a difference between the two groups. There's clearly an overlap - clearly quite a few enthusiasts are also spotters - but I've certainly spoken to quite a few spotters whose interest is too narrow for them to be enthusiasts.
I went on a railtour recently and got chatting to a few people of the "spotter" variety - nice enough guys, although from their conversation I gathered they weren't particularly interested in the wider operational aspects of the railway. The tour passed Gatwick airport and a few of them pulled out aviation magazines. Aviation is a huge passion of mine and I expected a good discussion about flying - but I soon realised their interest in aviation, as with the railway, was limited to compiling endless lists of aircraft types and registrations!
It seems to me that for these guys, the spotting is an end in itself. Perhaps it's the order, structure and compulsive nature of the activity that appeals to them.
To hobbyists whose interest is somewhat more inclusive; it does sometimes feel surprising how very narrowly and what can seem, in a pretty intellectually un-demanding way some in the hobby, choose to specialise; as with the referred-to spotter-only types. At times, I and other enthusiasts not "doing" such a degree of tunnel-vision, have similarly boggled at the most extremely single-minded variety of railway photographer who seemingly has no interest in railways, locomotives or trains, beyond ardently seeking to photograph (often with considerable artistic care) every rail vehicle that he encounters; without wanting particularly to know anything about said vehicle, and being quite likely never to look again at his photograph after hes taken it.
Still, one feels in a free country: if someone finds satisfaction from pursuing a hobby in a way which appears to others, narrowly hyper-specialised and wilfully ignorant about most aspects of it fair enough, they have that right. (Robert A. Heinlein said specialisation is for insects; but he dogmatically spouted a lot of utter nonsense on a variety of subjects.) I wonder occasionally whether some of us who congratulate ourselves on being greater generalists, are always on solid ground in doing so. My own enjoyment of the railway hobby, revolves chiefly around stuff in the past; Im ignorant (and for myself, content to be) in ways in which Id be ashamed to admit to in detail, about much concerning equipment and organisation on the current rail scene.