[Desire HD Q&A, Help & Troubleshooting] Ghazkul:
It can cause drain, but its not the AlarmManager in it self that is causing it, its the other apps that use it. Other apps use it to wake up on specific times or intervals, like if you have a weather widget that needs updating every 30 min or an application that checks your location every x min etc. Here are parts of my own AlarmManager dump and you might get the idea what I mean:

Alarm Stats:
com.google.android.gsf
20993ms running, 75 wakeups
4 alarms: act=com.google.android.intent.action.GTALK_RECONNECT flg=0x4
42 alarms: flg=0x4
29 alarms: act=com.google.android.intent.action.GTALK_HEARTBEAT flg=0x4

se.f1nally.snowstorm
547ms running, 11 wakeups
11 alarms: act=se.f1nally.yrvader.UPDATE_ALL flg=0x4 cmp=se.f1nally.snowstorm/.UpdateService

com.mobitobi.android.gentlealarm
2128ms running, 11 wakeups
11 alarms: act=com.mobitobi.android.gentlealarm.ALARM_ALERT flg=0x4

com.jb.gosms
45ms running, 1 wakeups
1 alarms: act=com.jb.schedule.private.box flg=0x4

com.blizzard.bma
2061402ms running, 0 wakeups
2611 alarms: act=android.appwidget.action.APPWIDGET_UPDATE flg=0x4

android
809072ms running, 281 wakeups
1 alarms: act=android.intent.action.DATE_CHANGED flg=0x20000004
9 alarms: act=com.android.internal.policy.impl.PhoneWindowManager.DELAYED_KEYGUARD flg=0x4
1138 alarms: act=android.intent.action.TIME_TICK flg=0x40000004
123 alarms: act=com.android.server.ThrottleManager.action.POLL flg=0x4
19 alarms: act=android.app.backup.intent.RUN flg=0x40000004
80 alarms: act=android.appwidget.action.APPWIDGET_UPDATE flg=0x4
173 alarms: act=android.content.syncmanager.SYNC_ALARM flg=0x4

com.liato.bankdroid
443ms running, 6 wakeups
6 alarms: flg=0x4 cmp=com.liato.bankdroid/.appwidget.AutoRefreshService

com.google.android.apps.maps
804ms running, 43 wakeups
43 alarms: flg=0x4 cmp=com.google.android.apps.maps/com.google.googlenav.prefetch.android.PrefetcherService

com.viber.voip
164775ms running, 618 wakeups
617 alarms: act=com.viber.voip.action.KEEP_ALIVE_RECEIVE flg=0x4
1 alarms: act=com.viber.voip.action.VERSION_CHECK flg=0x4

net.dinglisch.android.tasker
14114ms running, 104 wakeups
90 alarms: act=net.dinglisch.android.tasker.ANOFFCHECKORUM flg=0x4
14 alarms: act=net.dinglisch.android.tasker.ALARUM flg=0x4

de.devmil.minimaltext
6619ms running, 0 wakeups
64 alarms: act=updatetasker dat=minimaltextwidget://widget/id/updatetasker flg=0x4 cmp=de.devmil.minimaltext/.MinimalTextUpdateService
249 alarms: act=update dat=minimaltextwidget://widget/id/update flg=0x4 cmp=de.devmil.minimaltext/.MinimalTextUpdateService
59 alarms: act=forceupdate dat=minimaltextwidget://widget/id/forceupdate flg=0x4 cmp=de.devmil.minimaltext/.MinimalTextUpdateService
3 alarms: act= dat=minimaltextwidget:/weather/ flg=0x4 cmp=de.devmil.minimaltext/.weather.WeatherUpdateService
3 alarms: act=ForceUpdate dat=minimaltextwidget:/weather/ForceUpdate flg=0x4 cmp=de.devmil.minimaltext/.weather.WeatherUpdateService

org.koxx.pure_calendar
29ms running, 5 wakeups
5 alarms: act=org.koxx.pure_calendar.UPDATE_ALL flg=0x4 cmp=org.koxx.pure_calendar/.UpdateService

com.bigtincan.android.adfree
11231ms running, 1 wakeups
1 alarms: flg=0x4

It is part of the android os so thats why I dont think you can uninstall it. See this page for dev info on AlarmManager.