Scales over songs

I know multiple scales can be played over a certain chord/progression but is it ever the case that only one scale really fits?

for any progression there is at least one scale that can work on it. more sometimes too. but the weirder and more obscure the progression gets, the harder it is for a good scale to work with it. I guess if it is obscure enough, only one could truely work with it, but noone wants to listen to that anyways.

Basically, the simpler the progression, the more scalar freedom you have. If the progression is complex with lots of chords, you usually need to limit yourself to the appropriate scale or scales, otherwise your lead will sound completely out of whack. You can have a lot of fun experimenting with different scales over a basic chord progression, I find it's the easiest way to come up with new ideas for lead guitar.

Alot of Yngwie solos,as an example,employ the repetition of a single note/chord,while he improvises over the top of it.The less melodic the background chord sequence,themore freedom and variations are possible.Melody is achieved in two ways,by the accompaniment or the soloist,sometimes both. Lead guitarists prefer simple accompaniment,allowing them to dictate pace,content,and melodic direction.One case where a lead may be handcuffed to a single scale or pattern is diminished,no other scale or pattern really works other than diminished with diminished,which is probably why,other than Yngwie,it's not widely used.To summarize,a "busy" accompaniment is generally not advisable.