There shouldn't be any problem; spooling two films back to back has
been, at times and for some people, a standard method of getting two 120
films into a single 120 tank to obtain economy of chemical usage that
matches 35 mm.  I've even heard of it being done with 35 mm.

The film base has a gelatin "anti-curl" coating, but with most films
there's nothing coated onto or in that gelatin; antihalation layers are
under or in the emulsion, on the emulsion side (they have to be, in
order to protect from reflections and light piping inside the base), and
the base coloration is in the plastic material of the base itself, not
coated on.  Worst case, if you find a particular emulsion gives trouble
that way, you can rewash the film and will most likely remove any dyes
that might be present in the anti-curl coating.  However, be certain you
separate the films for drying; the anti-curl coating is thin, but more
than sufficient to glue two strips together, back to back, for eternity.

The possibility of fixer remaining in the anti-curl coat is a concern,
however, with or without wash aid; it would probably be preferable to
separate the films for washing.  Worthy of note here; if you use an
alkaline fixer like TF-4, washing can be as little as five minutes for
archival removal of fixer (though longer wash may still be preferred to
promote stain formation); that's not too long to spend periodically
separating the films for flow between, since you'll probably spend twice
that long just in the developer.