In general, If there is a halachic doubt as to whether to say a bracha it is better to answer Amen to someone else's bracha then to say it yourself. This way you avoid the possibility of making a bracha levatala. This is done Shavuos morning: someone who slept will be motzi those who stayed awake with birchos hatorah, elokai netzor and ha'maavir shaina. (Mishne Berurah 47:28)

Furthermore, it is permissible to answer amen to a bracha for which there is a machlokes haposkim as to whether one should be making that bracha. (Biur Halacha 216 s.v. ve'asur)

In this case, the issue of making a bracha and or saying hallel on Yom Ha'atzmaut is very contentious and many will opine that there is no doubt that a bracha is not sanctioned and this is not an area if doubt. In fact, the Biur Halacha (ibid), specifically states that one is allowed to answer Amen only to a bracha whose provenance is well established and not based on a rejected opinion. Undoubtedly, others will assert that a bracha in this context is appropriate.

As always as you personal halachic authority.

In general, If there is a halachic doubt as to whether to say a bracha it is better to answer Amen to someone else's bracha then to say it yourself. This way you avoid the possibility of making a bracha levatala. This is done Shavuos morning: someone who slept will be motzi those who stayed awake with birchos hatorah, elokai netzor and ha'maavir shaina. (Mishne Berurah 47:28)

Furthermore, it is permissible to answer amen to a bracha for which there is a machlokes haposkim as to whether one should be making that bracha. (Biur Halacha 216 s.v. ve'asur)

That Biur Halacha, specifically states that one is allowed to answer Amen only to a bracha whose provenance is well established and not based on a rejected opinion. Thus if one follows the opinion that making a bracha on Hallel is a bracha levatala and the opinions to make a bracha are without merit, one may not answer Amen to a bracha on Hallel. Otherwise, one may answer Amen.

As always ask you personal halachic authority.

In general, If there is a halachik doubt as to whether to say a bracha it is better to answer Amen to someone else's bracha then to say it yourself. This way you avoid the possibility of making a bracha levatala. ( this is done dhavuis morning where someone who slept will be motzi those who stayed awake with bruchos hatorah. See mishne berurah 47:28

Furthermore, it is permissible to answer amen to a bracha for which there is a machlokes haposkim as to whether one should be making that bracha. Biur Halacha 216 sv veasur

In this case, the issue of making a bracha and or saying hallel on yom haatzmaut is very contentious and many will opine that there is no doubt that a bracha is not sanctioned and this is not an area if doubt. Undoubtedly, others will assert that a bracha is appropriate.

As always as you personal halachik authority.

In general, If there is a halachic doubt as to whether to say a bracha it is better to answer Amen to someone else's bracha then to say it yourself. This way you avoid the possibility of making a bracha levatala. This is done Shavuos morning: someone who slept will be motzi those who stayed awake with birchos hatorah, elokai netzor and ha'maavir shaina. (Mishne Berurah 47:28)

Furthermore, it is permissible to answer amen to a bracha for which there is a machlokes haposkim as to whether one should be making that bracha. (Biur Halacha 216 s.v. ve'asur)

In this case, the issue of making a bracha and or saying hallel on Yom Ha'atzmaut is very contentious and many will opine that there is no doubt that a bracha is not sanctioned and this is not an area if doubt. In fact, the Biur Halacha (ibid), specifically states that one is allowed to answer Amen only to a bracha whose provenance is well established and not based on a rejected opinion. Undoubtedly, others will assert that a bracha in this context is appropriate.

As always as you personal halachic authority.