Small municipalities pool their resources, at least around my area.
The only voluntary service we have is the Red Cross and Protección Civil.
I'm not 100% sure on this, but professional emergency services are definitely common.
I've got a friend who's an occasional firefighter in Belgium, in addition to his regular job. He's not an unpaid volunteer: I don't know how it works exactly regarding the pay but I know that once he'll reach the age where he'll stop working, he'll get two monthly pensions paid (the regular one + one because he was a firefighter).
Which is why only officers have a base comp' above the minimum legal salary, the lowest rank gets 8.08 (euros) (the minimum legal salary is 10.25), but it's tax-free.
And that's on active duty (which doesn't necessarily mean on-site, it might be training or admin or whatever), when on-call it's generally half-that (legally anyway, some places give volunteers more).
We have reserves of volunteers for emergency health care and so on (for example they're being used for vaccination right now), working on the same principles as the ones you have described.