But what is not possible, is to have a cell start with a subparagraphs (such as 1.1 or 1.1.1). If you write the following:
Then the software will think you made a mistake in the 1.1, and treats it like a 1. instead.
The underlying technical reasons are the following:
The initial numbering (1., 1.1., 1.1.1.1, etc.) of a paragraph is plainly ignored within cells, so if you start a cell with such numbers, then they will be hard-coded as such, instead of treated as automatic numbering.
However, you can perfectly have initial numbering within a snippet. So if you refer to a snippet within a cell, you can partially get what you want.
Each snippet is separately analyzed. So a snippet for which the paragraphs start with 1.1., will be unaware of other snippets that have a paragraph starting with 1. And when the software looks at the snippet containing 1.1, it will treat your 1.1 as the top level.
Also be aware that within a table, it is somewhat unpredictable in which order MS Word will take up the numbering.