It is, however, true that SLES is less conservative than e.g. RHEL when it comes to bumping software versions between their minor releases (service packs). I remember that they switched from 2.6 to 3.0 kernels sometimes in SLES10 days. Fun stuff.
The link you posted only states that the upgrade is not supported for 64-bit ARM, and that 32-bit (x86) system cannot be upgraded to Leap. It doesn't say upgrade in general is not.
tumbleweed does or rather, tumbleweed does not have point releases. in my eyes tumbleweed is way better for cloud, IoT and desktops, as soon as you use transactional-update
