It's necessary to confirm whether it would be fine to purchase the product of a rival company.
It's necessary to know if it would be allowed to purchase the product of a rival company.
ご質問ありがとうございます。
「ライバル会社の製品を購入できるのか確認する必要がある」は英語で「It's necessary to confirm whether it would be fine to purchase the product of a rival company.」と言えます。
「to know if」でも使えます。
その場合、「It's necessary to know if it would be allowed to purchase the product of a rival company.」になります。
正直に１つ目の英文の方が自然ですが、2つ目の英文を使えます。
ご参考になれば幸いです。
"We need to make sure it's ok to purchase the products of our competitors."
"We need to check to make sure it's ok to buy our competitors products."
- "We need to make sure it's ok to purchase the products of our competitors."
"we need to make sure ~" 「〜を確認する必要がある」
"it's ok to ~" 「〜できるのか」"we can" も言えます。
"to purchase ~" 「〜を購入」"to buy" も言えます。"purchase" の方がフォーマルな言い方です。
"the products of our competitors" 「ライバル会社の製品」"our competitors products" も使えます。
"competitors" 「ライバル会社」
- "We need to check to make sure it's ok to buy our competitors products."
"to check ~" 「〜確認する」・「〜調べる」
アメリカ合衆国 
オーストラリア 
