Will he be rewarded for dhikr of the tongue when his heart is not focused?

Dhikr-Allaah
(remembrance of Allaah) is one of the greatest of good deeds and the best of
actions by means of which one may draw closer to Him. There are dozens of
texts which speak of its virtues, enjoin it and encourage it, such as the
words of the Prophet (peace and blessings of Allaah be upon him):
“Shall I not tell you of the best of your deeds, the most pleasing to your
Sovereign, those that raise you most in status, and that are better than
your giving gold and silver, or meeting your enemy (in battle) and you
strike their necks and they strike you necks?” They said: “Yes,” He said:
“Remembrance of Allaah (dhikr), may He be exalted.” Narrated by al-Tirmidhi
(3373) and Ibn Maajah (3790); classed as saheeh by al-Albaani in Saheeh
al-Tirmidhi. 

The most
perfect of dhikr is that in which the heart and tongue are both focused,
then that which is in the heart only, then that which is on the tongue only.
In all cases there is reward, in sha Allaah. 

Al-Nawawi
(may Allaah have mercy on him) said: Dhikr may be in the heart, or on the
tongue, but the best is that which is both in the heart and on the tongue.
If it is limited to just one of them, then the heart is better. End quote
from al-Adhkaar (p. 20). 

But those
who understand spiritual matters have drawn attention to the fact that dhikr
which is limited to the tongue only and not the heart is of little value and
that it is little benefit. Ibn al-Qayyim (may Allaah have mercy on him)
said: The types of dhikr may be in the heart and on the tongue sometimes,
which is the best of dhikr, or they may be in the heart only sometimes,
which is the second level, and on the tongue sometimes, which is the third
level. The best of dhikr is that on which both the heart and tongue are
focused, and dhikr in the heart only is better than dhikr on the tongue
only, because dhikr in the heart increases knowledge, provokes love,
increases shyness before Allaah, promotes fear of Allaah, calls one to draw
closer to Him, and it prevents one from falling short in acts of worship and
being heedless about sins and bad deeds. Dhikr on the tongue only does not
give any of these results and it is of little benefit. End quote from
al-Waabil al-Sayyib min al-Kalim al-Tayyib (p. 120). See also
Madaarij al-Saalikeen (2/420) 

We ask
Allaah to make us among His slaves who remember and thank Him, and to help
us to remember Him, thank Him and worship Him properly. 

And Allaah
knows best.