The French Adrian helmet had a rather distinct ridge crest. In many manufacturers' figures this is rather noticeable.
Good for Belgians, not so good for Dutch.
As mentioned the Dutch used the same helmet as the Romanians. It had a somewhat pronounced extension in the back (down over the neck). This characteristic is somewhat exaggerated on the GHQ figures, making the helmets look somewhat over-sized compared to many other figures. It's not at the level of giant-headism that is sometimes seen in other manufacturers, so it may be fine from your perspective.
Italian and Polish helmets are much more generic is shape. You could use them for almost any nation and there is nothing noticeable in the helmets (unless it is the lack of something noticeable).
You may want to also considering other things, like the weapons, webbing, etc.
I find I can rarely distinguish rifles at this scale, even when I'm being picky. So I don't worry about those.
LMGs are somewhat more distinctive. Romanians used their own derivative of the Czech Brno LMG (which was also the basis for the British Bren). The GHQ Romanians have this gun, which is nicely modeled. At this scale I find it indistinguishable from a French FM29 LMG. But otherwise it is somewhat distinctive.
The Belgian army used their own version of the BAR. You might get a reasonable stand-in by simply shaving off the top-mounted magazine of a French (or Romanian) LMG. The Poles also used their own version of the BAR, but in that case you don't get the helmet you want for your Belgians.
I really don't know what the Dutch army used for an infantry LMG. I believe they had some Lewis guns (including some in 6.5mm rimmed caliber) and some Johnson LMGs (with a side-mounted curved box magazine). You might consider using a Russian LMG figure for your Dutch army if you want to model a Lewis gun -- the magazine has a larger diameter than you want, but it is at least round. The barrel will also be thinner than you want. But it's about the only choice for a stand-in for a Lewis. No ideas about a Johnson.
The GHQ Romanians include a fair number (not all, but some portion) of figures wearing their rolled overcoats diagonally across the shoulder in the same style as Russians. This is somewhat out of place for Dutch infantry. But you might mitigate that oddity just by how you paint them, to make the rolled coat look more like a part of the web gear.
Here is a picture of one of my Romanian infantry squads.
Here is a picture of one of my French North African infantry squads.
I use the GHQ Romanian figures for both my Romanian force and for my French North Africa force. The weapons are similar enough (LMGs and light mortars). I use the somewhat oversized helmets serve as tropical sun helmets (used by some, but not all, in the Armee d'Afrique). And I paint the rolled coats as if they were just suspenders in the webbing.
Hope that helps.
-Mark
(aka: Mk 1)
looks at another D-Day: German set for Flames of War.
