I've done this when I beach my boat for bottom scrubbing or when I'm on a
"Grid". (If I'm on a Grid, there is usually a set of pilings to lean
against on one side but it is still a good idea to run a halyard off that
side to make sure she has a list in the direction of the piling as the tide
goes out.)

You should be ok on the hard, however it might depend on how your boat is
built. If it is an older wooden boat, you may need the support of stands to
help keep her shape. The frame and keel structure relies on support
distributed over the entire under water surface, not just the keel. The keel
should support only about 50% while the side supports the remainder.. (this
is a general rule of thumb for steel ships in dry dock.)

If your boat is fiberglass and has a fin or attached keel, you also should
be using a cradle of boat stands. Even then you need support of the stem and
stern.

There should be no problem using the mast and rigging to keep the boat
upright, as long as she is landed and maintained in a vertical conditions. I
wouldn't recommend moving a lot of fuel or weight around if your just
holding her with halyards.

--
My opinion and experience. FWIW

Steve
s/v Good Intentions