It all depends on what your comfort level is with various things.

We have two of our servers with National Net, and three others spread out among two other providers.

Our gallery server is with a low-cost provider. It's an unmanaged box, but it also costs probably about 1/3 of what a managed hosting provider like NatNet would charge. I do all the basic admin with it, and so far, the provider has been excellent about providing quick support where needed. We do our own server monitoring on all of our boxes, so we know immediately if a box is down, and we do have to use a contracted tech consultant every now and then, but even with those costs factored in, it's a lot cheaper simply because it uses so much bandwidth. Yes, the off-brand bandwidth is probably a bit slower, but I've never had a complaint from an affiliate, and we track things pretty carefully as far as load times and uptime.

I absolutely believe that having critical boxes with a provider such as NatNet makes a lot of sense, but to be honest, we've had maybe 6 hours of downtime in the past 2 years with the low-cost provider, which includes fixing a failed hard drive and reloading the server, so that's still better than 99% uptime.

One solution might be to put the gallery services on your gallery server, but have a backup version ready to roll on your NatNet server so if something goes wrong with the gallery provider, you can change the entry in DNS and be pointing to your NatNet server within a few minutes.