This is a really tricky one that I can’t give you a definitive legal answer on, but…
If we make something ‘official’ we have to have it approved. So if we liked a thing you made we’d have to approve it before we put it on our site to offer ‘via Modiphius’.
As this is a public forum I believe you are allowed to post anything that helps the game under the usual rules any forum has about being nice and not bringing the subject into disrepute. But thats the same for forum posts as much as added resources.
The tricky part is collating and reprinting sections from published works.
As gamers we generally support anything that helps people play the game as long as you don’t make it unnecessary to buy the Core rulebook (or any other published works). So, putting the character generation chapter up on a website is a no, but creating a summary or character generation for your own rules guide is usually ok.
As a company we can’t condone or offer permission to reprint any part of any published work.
So, because of that dichotomy I can’t give you a definitive answer.
(and I’m unqualified to offer a legal answer, or an official company position)
But as a general guideline, if you make us aware of anything you post (such as by asking permission, or posting it here) we can ask you to remove it if by some chance it proves to be something we cannot allow (and we’d like to be aware of cool stuff people are doing).
However, after rambling I also notice you are talking specifically about a Virtual tabletop. We currently have a fair few of these in production with several different platforms. So, if you talk to the marvellous Lloyd through out customer service email he may be able to tell you if the platform you are considering is already in process or if there are any specific guidelines.