A resposta à sua pergunta específica é NÃO , o Active Directory não permite espaços nos nomes de host do DNS. Os caracteres proibidos estão claramente descritos no KB 909264 - Convenções de nomenclatura no Active Directory para computadores, domínios, sites e UOs no seção marcada como Caracteres não autorizados :
The DNS host name cannot contain blank or space characters.
Para estender a resposta além do Active Directory para o sistema de nomes de domínio DNS, em geral, a situação é um pouco mais complicada, pois embora os espaços tecnicamente sejam permitidos em certas instâncias, na prática, você provavelmente nunca encontrará esse caso.
A resposta curta: NÃO USE ESPAÇOS EM HOSTNAMES DE DNS!
A resposta longa de acordo com §2 da RFC 3696, Restrições de nomes de domínio (DNS) é isso:
Any characters, or combination of bits (as octets), are permitted in
DNS names.
Continua afirmando (ênfase minha):
However, there is a preferred form that is required by most
applications. This preferred form has been the only one permitted in
the names of top-level domains, or TLDs. In general, it is also the
only form permitted in most second-level names registered in TLDs,
although some names that are normally not seen by users obey other
rules. It derives from the original ARPANET rules for the naming of
hosts (i.e., the "hostname" rule) and is perhaps better described as
the "LDH rule", after the characters that it permits. The LDH rule, as
updated, provides that the labels (words or strings separated by
periods) that make up a domain name must consist of only the ASCII
[ASCII] alphabetic and numeric characters, plus the hyphen. No other
symbols or punctuation characters are permitted, nor is blank space.
If the hyphen is used, it is not permitted to appear at either the
beginning or end of a label. There is an additional rule that
essentially requires that top-level domain names not be all-numeric.
Na prática, isso significa que você deve NÃO usar espaços , mesmo que na especificação mais geral de nomes de domínio, conforme definido nesses trechos de §5.1 do RFC 1035 é possível permitir espaços em nomes de domínio:
<domain-name>s make up a large share of the data in the master file.
The labels in the domain name are expressed as character strings and
separated by dots. Quoting conventions allow arbitrary characters to
be stored in domain names.
e
<character-string> is expressed in one or two ways: as a contiguous
set of characters without interior spaces, or as a string beginning
with a " and ending with a ". Inside a " delimited string any
character can occur, except for a " itself, which must be quoted using
\ (back slash).
Lembre-se de que em outras partes da RFC 1035, especificamente §2.3 , ela avisa:
2.3. Conventions
The domain system has several conventions dealing with low-level, but
fundamental, issues. While the implementor is free to violate these
conventions WITHIN HIS OWN SYSTEM, he must observe these conventions
in ALL behavior observed from other hosts.
2.3.1. Preferred name syntax
The DNS specifications attempt to be as general as possible in the
rules for constructing domain names. The idea is that the name of any
existing object can be expressed as a domain name with minimal
changes.
However, when assigning a domain name for an object, the prudent user
will select a name which satisfies both the rules of the domain system
and any existing rules for the object, whether these rules are
published or implied by existing programs.
For example, when naming a mail domain, the user should satisfy both
the rules of this memo and those in RFC-822. When creating a new host
name, the old rules for HOSTS.TXT should be followed. This avoids
problems when old software is converted to use domain names.
Eu certamente gostaria de receber mais esclarecimentos ou correções na minha interpretação, mas por favor, não o faça, a menos que você seja capaz de citar seções específicas de RFCs para afirmar ou negar essa interpretação.