No. Belgian Tervurens are not hypoallergenic. Their heavy double coats shed and leave pet dander in your home. Pet dander is the primary cause of pet-related allergies.
Tervurens are naturally protective of their family members and will become aggressive if they sense their people are in danger. They may be confused about what constitutes a threat when they don't learn this at an early age through socialization. When well socialized, they are not aggressive. Don't expect them to be gregarious, however. Tervs are naturally reserved around strangers.
Belgian Tervurens can learn to swim and many enjoy going into the water on a hot day. All dogs have different preferences, however, so let your Terv take the lead. If he doesn't seem very interested in swimming, don't force the issue. All dogs should be watched closely while swimming.