Use of gas detecting paint is common on other types of WW2 Polish exile helmets as well. HOWEVER, I also want to point out that plain yellow paint (or in some cases white paint) was regularly used for Polish helmet eagles. There are some collectors who dismiss Polish helmets with yellow eagles in anything but gas detecting paint, but they are wrong to do so. There are numerous examples of eagles in plain old non-gas detecting yellow paint of varying shades, and as I like to paraphrase Freud's comment about cigars.... sometimes yellow paint is just yellow paint. And its use in the application of a Polish helmet eagle does not in and of itself indicate a forgery. But of course, knowing that a certain type of helmet had predominantly a certain type of eagle or a certain type of paint used on the eagle, would go to the weight of the evidence.
So the answer to your question is: yes and yes. I do believe that gas detecting paint was actually employed for that purpose, but also, the Poles used whatever paint supplies they had at hand, and that is in evidence on numerous extant specimens.
Finally, for those interested in the topic, there is a thread on the Polish Exile forces section of the forum dealing with Polish Exile Helmet Eagles.