Yes, if you are otherwise able to claim him as a dependent, a dependent who is gone for a "temporary absence" would still be able to be claimed on your return. When answering the question to the number of months lived with you, you will include those months while he is temporarily away.
The IRS defines temporary absence as follows:
"A nonpermanent failure to occupy a home by reason of illness, education, business, vacation, military service, institutionalized care for a child who is permanently and totally disabled, or incarceration may be treated as a temporary absence due to special circumstances. This definition of temporary absence applies to the residency test for a qualifying child, to the relationship test for a qualifying relative who does not have a listed relationship to the taxpayer, and to the requirements to maintain a household for surviving spouse and Head of Household."https://apps.irs.gov/app/vita/content/00/00_19_010.jsp?level=a
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