In my (very recent) experience, Elecrow are fine with multiple boards in their 5 x 10cm etc deals, as long as you only separate the boards on the ident, and don't expect them to rout them or otherwise separate them. I've always done this bit myself and sent them a single 'unified' gerber set. I tend to leave 2.5mm or 100th between designs.
This is fine for prototypes - no problem to separate with a hacksaw and file / router / big Aussie knife - but obviously no good for production.
sca