Not a silly question at all - a very good one, in fact!
These toys are getting old now, and the plastic can get brittle with age. Heck, even back in the '80s, if you played with a certain figure a lot, you'd end up with broken thumbs if you're not careful (alas, my poor '85 Snake Eyes).
I love posing my classic Joes with all their gear too, when possible. Sometimes (especially the later ones) they've just got too much stuff. Other times - and this is what you might be afraid of, I think - you've got to watch out for certain figures, certain weapons, etc. Genereally, I would avoid placing gunstocks tucked under the arm, unless the grip of the figure in question has already been loosened up a bit... and I would absolutely not try to "loosen up" the grip of a vintage figure myself, btw! But sometimes we kids did it back in the '80s.
Here are a few examples: V1 Spirit.
The handle on his gun is quite thick. Unless your figure's thumbs have been "worked in" back in the '80s, I wouldn't dare put it in his hands. Even then, I'd be careful, particularly if your Spirit is nice and minty. A truly mint Spirit is difficult to find, because of those gold bands on his wrists... Be a real shame to break one that doesn't have wear. I still pose him with all his stuff, but at the "order arms" position. A bit tricky to do but better than a broken figure. Belts, etc.
On the subject of Spirit... I would be wary of any of the rubber belts/straps that figures came with, especially in '84, it would seem (e.g. Spirit's belt, Mutt's gas mask, Blowtorch's mask, etc.). They can get brittle and crack. It might be worth boiling some hot water and getting them soft before putting them on, and maybe inspecting them regularly. Footloose's M-16 strap (and others).
I've had one of these break simply because it was shouldered. I didn't think there was any pressure on it, but apparently there was... just something to watch out for. This happened to my Outback as well. Uzis.
Seems like all of these are particularly prone to handle wear. This is a lot more common on figures that have been obviously played with/handled by us '80s children back in the day. You should be fine with the '82 Snake Eyes/Steeler Uzi and '85 V2 Snake Eyes Uzi if you're careful, but as far as the one that came with V1 Lowlight/Law and Order... if the grip on those figures are tight at all, I wouldn't even use it. If you look at the handle, you'll know what I mean - you'll tear that thing up. Again, not a problem if the grip on those figures have been "worked in", but if they're like they were right out of the package, watch out.
That's what I can think of off the top of my head... If more examples come to me, I'll post 'em.
Also, not directly relating to posing w/accessories, but worth mentioning: V1 Duke, Doc, Tripwire... and I think Zartan too, from what I've heard.
Something about the boot/heel design makes these figures especially prone to broken heels, if you use a figure stand or place them on a peg on a vehicle or playset (I bought a Chinese version of Duke specifically so I could pose him with a stand - my original goes in the passenger seat of my Dragonfly). Crotches.
V1 Duke and Beachhead are particularly prone to broken crotches. Of course this can apply to any figure, but the ones used on these (and probably some others I'm not aware of) were particularly thin for some reason.