For the purposes of effects that search a zone for a card with certain characteristics (such as found in Recruiter of the Guard), what is relevant are the characteristics that card has in that zone, not necessarily what those characteristics would be elsewhere.
In this sense, effects from characteristic-defining abilities (such as Geist-Honored Monk's second ability, which has the form "[This creature's] power and toughness are each equal...") generally work differently from effects of the form "get[s] +N/+M" or "get[s] -N/-M" on static abilities (such as found in Serra Ascendant and Death's Shadow). The former work everywhere, including in libraries, and the latter generally work only on the battlefield (C.R. 604.3, 604.3a, 611.3b, 112.6, 112.6a). See also this thread.
Therefore—
Serra Ascendant's toughness in your library will be 1 regardless of your life total, so it can be searched for with Recruiter of the Guard's ability, and
Geist-Honored Monk's power and toughness in your library will each be equal to the number of creatures you control (C.R. 109.5), so it can't be searched for with Recruiter of the Guard's ability in this scenario since its toughness is 5 in this scenario.
Note also that Recruiter of the Guard's ability doesn't target anything (it lacks the word "target" or a keyword that uses that word, for example) (C.R. 114.1d, 114.10, 114.10a).
To summarize:
While it is in your library, Serra Ascendant is a 1/1, because its +5/+5 ability is 'inactive', as per rule 604.2.
While it is in your library, Geist-Honored Monk does count your creatures, because its power/toughness ability is 'active', as per rule 604.3.
604.2. Static abilities create continuous effects (…). These effects are active as long as the permanent with the ability remains on the battlefield (…)
604.3. Some static abilities are characteristic-defining abilities. (…) Characteristic-defining abilities function in all zones. (…)
Play Recruiter of the Guard. Assume my life total is 40 and I have 5 creatures out on the battlefield (including Recruiter of the Guard)
Are Serra Ascendant and Geist-Honored Monk valid targets from your library?
Thanks!
In this sense, effects from characteristic-defining abilities (such as Geist-Honored Monk's second ability, which has the form "[This creature's] power and toughness are each equal...") generally work differently from effects of the form "get[s] +N/+M" or "get[s] -N/-M" on static abilities (such as found in Serra Ascendant and Death's Shadow). The former work everywhere, including in libraries, and the latter generally work only on the battlefield (C.R. 604.3, 604.3a, 611.3b, 112.6, 112.6a). See also this thread.
Therefore—
Note also that Recruiter of the Guard's ability doesn't target anything (it lacks the word "target" or a keyword that uses that word, for example) (C.R. 114.1d, 114.10, 114.10a).
EDIT (Apr. 13): Correctness edit; add rule citations.
While it is in your library, Serra Ascendant is a 1/1, because its +5/+5 ability is 'inactive', as per rule 604.2.
While it is in your library, Geist-Honored Monk does count your creatures, because its power/toughness ability is 'active', as per rule 604.3.
604.3. Some static abilities are characteristic-defining abilities. (…) Characteristic-defining abilities function in all zones. (…)
RULES OF MAGIC :
http://magic.wizards.com/en/game-info/gameplay/rules-and-formats/rules