You can test it.
You can check the docs too, however, I believe you cannot "technically" do that. But test it.
If you have thousands of SFDC users, however, the token may not resolve quickly and cause it to time out.
I am 100% sure it's not possible
I have listed this in quite a few, complementary ideas gathered here: Marketo / salesforce integration needs a serious overhaul, don't you "sync"?
that together would enable to set up very sophisticated assignment.
- Sync all Lead/Account/Contact related users
- Use any lookup field containing user info to assign leads on a "sync lead" or "change owner" flow steps
- Use the owner of any related object to assign leads in CRM
- Use tokens in the "sync lead to SFDC" and "Change owner" flow steps