There is a big difference between "Can" a machine do something and "Should this machine be used to do a specific task."? The easiest way to determine this is to see if John Deere offers the specific item or implement for the machine required to complete the task.
In the case of the X350, there is NOT a rototiller attachment offered through the "Build and Price" program through John Deere. However, There IS a front snow blower and snow plowing adapter kit offered, to make the machine capable of clearing snow.
I have a neighbor who mows a very hilly lawn and who uses a snow blower on the front of their x354 and has for 4 years. It gets the job done. The overall results aren't like those of a higher quality machine, but it completes the tasks.
John Deere doesn't offer a rototiller for the x350 machine, therefore, I certainly wouldn't either adapt one to fit or use an after market tiller.
In the case of snow removal, that is an entirely different task. How different is it? Well, if you have ever used a shovel to turn the soil in a trench 3' wide and 8" deep and the length and width of an intended garden, than you know the effort required to do so. Same thing with shoveling snow. Is the effort to shovel 8" of snow the same as it is to dig a trench or turn soil to an 8" depth? Hardly......
John Deere is warrantying new machines based upon how they are expected to be used by owners. Also, the machines warranties are as follows;
The x3xx is 48 months or 300 hours, whichever comes first (WCF)
The x5xx machines, the warranty is extended to 48 months or 500 hours, W.C.F..
The x7xx machines, the warranty is 48 months or 700 hours of use , W.C.F.
The x500 and x700 can and do offer both snow blowers and roto tillers. The X350 offers snow removal equipment, but no ground tilling equipment. Which is good. Simply follow the manufacturers recommended suggested use for the equipment and its usually a much better ownership experience.