My question is, from the company's network can I connect to this client, access the data from his machine?

The needed data are on the client machine itself, as I understand? Accessing the network behind the client was more complicated and would need a client specific override, when running an access server.

You can access the client itself simply by its virtual IP. You can add a SCO anyway to assign a static virtual IP to him.
But you have to allow the access on the clients firewall at all.

A trick I'm using for Windows clients to enable access to them is pushing the default route to them, but with a high metric by adding this into the servers custom options box:

push "route-metric 512";push "route 0.0.0.0 0.0.0.0"

This makes the client "smooth", but networking has to be enabled on the client anyway.
However, consider that the pushed metric is applied to any route which is pushed to the client, but worked well.