A. Ibn Taymiyya was asked the same question in his Fatawa and he replied in the affirmative, citing the narration whereby `Ali ibn Abi Talib said to Umar ibn al-Khattab: sallallahu `alayka ya `Umar -- "Blessings of Allah upon you O `Umar."
It is noteworthy that the Shi`a refuse to invoke blessings on the wives of the Prophet, although the Prophet specifically told the Companions to do so. When the Companions asked the Prophet how they should invoke blessings on him, he said:
Say: "O Allah, bless Muhammad, his wives, and his offspring as you blessed Ibrahim; and further grant blessing on Muhammad, his wives, and his offspring, as you granted blessing on Ibrahim. Verily, Yours is all the Majesty and Glory."
It is narrated by Bukhari with two chains, Nasa'i, Abu Dawud, Ahmad, Ibn Majah, and Malik.
It is known also that the Prophet invoked blessings on many of the Companions, such as Jabir ibn `Abd Allah, the family of Ibn Abi Awfa, the family of Sa`d ibn `Ubada al-Ansari, and others.
Allah Himself sent blessings on the Companions:
33:41-43: O you who believe! remember Allah, remembering frequently, and glorify Him morning and evening. He it is Who sends His blessings on you, and (so do) His angels, that He may bring you forth out of utter darkness into the light; and He is Merciful to the believers.
Furthermore, Allah ordered the Prophet to invoke blessings on his Companions:
9:103: Take alms out of their property, you would cleanse them and purify them thereby, and pray for them [lit. invoke blessings on them]
Those who restrict salawat resemble the beduin in Sahih Muslim who said: "O Allah, bless Muhammad and me, but do not bless anybody else." To which the Prophet replied: "O man, you have limited and narrowed something very vast." As for preferring anyone from the succeeding generations to the Companions of the Prophet, who are the best of all people after the Prophets, then they should ponder. Ibn al-Mubarak's affirmation that "The dust in the nostrils of Mu`awiya's horse is better than `Umar ibn `Abd al-`Aziz" just because Mu`awiya is a Companion of the Prophet, while `Umar ibn `Abd al-`Aziz is not. This is reported in Ibn Hajar al-Haytami's al-Sawa`iq al-muhriqa and by others.