Strictly speaking, and only looking at that one particular
"obstruction" rule, I would suggest yes.
However...
Also remember about the Captain's Clause and Event Organizer sections
of the rules (I.C., and I.D., respectively).
If the captain's are semi-permanently erecting structures in this are,
and both teams are agreeing (implicitly or explicitly) to play with
these items in this space, I'd suggest that perhaps this is an example
of the Captain's Clause being used, even though they didn't use the
words, "is it okay to play with this tent near the field?". If teams
have been playing a number of points, I'm not sure I'd agree that it's
appropriate to call obstruction and get it moved. Talk about it at the
beginning of the game, or I suggest you're implicitly agreeing to it
being there for the game.
And if the Event Organizers are putting fields closer together and not
explicitly saying what effect that may have to the 3m and 5m lines,
then this lack of clarity also negatively impacts situations such as
this. But of course, hindsight is usually 20/20.
It's different if it's players encroaching on the line when you're
trying to throw it up the line and they're not moving, but I view semi-
permanent structures that have been there for the entire game as
similar to fixed trees that are part of the OB area.
M