I realized that if we look at תוספות on בבא מציעא פ''ב ע''ב that both רש''י and תוספות come out fine. It is only the ר''ף and רמב''ם that I am having trouble understanding. For according to תוספות, ר' יצחק holds a lender with the pledge is a שומר שכר. So, the גמרא intended to say that ר' עקיבא and ר' אליעזר disagree about a case when the lender received the pledge at the time of the loan. To ר' אליעזר, he is an unpaid guard, and to ר' עקיבא he is a paid guard. However, if the lender received the pledge at a different time from the time of the loan, the lender is a paid guard according to both since in that case both agree with ר' יצחק. However, רש''י holds the lender is a שואל. Therefore, the גמרא intends that if the lender received the pledge at a different time than when he gave the loan, he is a borrower. But if he received the pledge at the time of the loan, to ר' אליעזר, he is an unpaid guard, and to ר' עקיבא he is a paid guard.