The L series loaders can do modest digging down into the ground. Most people advise against newbies using their loaders to do things like dig a pond or dig a long trench because loaders are not designed to do major digging projects, they are generally capable of doing limited digging into the ground, and there is no problem with any brand of loader digging into a pile or a mound.
Now some brands, particularly the Jinma varients from China, are known to break things when they are used for digging. I've only seen people complain of failures of front ends, in 4x4, on Jinmas. Also bear in mind that many tractors have loaders that are not OEM loaders, so if a tractor and a loader are mis-matched then potential for failure is greater. In your case you have a matching tractor and loader.
I think the problem with "digging" is that it means different things to different people. The type of digging you are doing is not an issue, your tractor can easily handle that amount and that type. Most loaders are capable of doing some very limited digging tasks, some are capable of modest digging. The "L" series Kubota is clearly one of the most capable tractors on the market and it is capable of modest digging. But if you asked if you should use your loader to dig a 1/2 acre pond, then I would say that you are going to tear apart your tractor and you should not use a loader for digging.