Yes you can designate these as your HBP. 

Your group RRSP contributions are treated the same as "usual" contributions for tax purposes. Like any other RRSP, you'll have no tax consequences until you withdraw the funds, except any employer's share is included as a taxable benefit on your T4.

@TurboTaxJennifer I think this question is around repayment, rather than withdrawal and I have the same question. As Group RRSP contributions are pre-tax unlike regular RRSP contributions, if we designate those to HBP repayment, will that be added back to the taxable income and therefore increase total tax? 

I am assuming any designations to HBP repayment, will not be having tax benefits like regular RRSP contributions because, we already got that benefit when we contributed to RRSP before withdrawing for HBP. Please clarify the same.

Group RRSP means that the employee contributes some, then the employer matches and contributes as well. the tax payer can designate from his portion only. the employer's portion will be received as income at retirement.

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